dissenting.
This case concerns an experienced tractor operator bypassing a tractor’s starting circuitry and starting the engine by shorting across the electrical contact points on the starter motor with a metal object, a screwdriver. One of the inherent dangers of this procedure is that someone must stand in the path of the tractor’s rear wheels. After reviewing the evidence, it is my view that the court’s instructions to the jury were supported by the evidence and the law. I respectfully dissent.
I agree with the majority that it is important to identify the theory of the case presented by plaintiff-appellant (McMur-ray). See Majority Opinion at 1438 n. 2. The majority then explains the premise of that theory — “that an ordinary consumer, after becoming familiar with the tractor, would believe it could only be started in neutral. An ordinary consumer would not understand that the neutral start switch would not function if the tractor was bypass started.” Id. This refinement of McMurray’s theory, with its emphasis on an ordinary consumer’s reliance on the neutral start switch, is not consistent with the emphasis in McMurray’s own description of the alleged defective condition.
Plaintiff contended that because the tractor could be started in gear by using the bypass starting method, and because no warning of this potentiality was given, the tractor was defective and dangerous beyond the contemplation of the ordinary user possessing ordinary knowledge of the tractor.
Plaintiff contended that Decedent’s death was a direct result of the defective condition of the tractor, and that Defendant was therefore liable for compensatory damages.
Plaintiff-Appellant’s Brief at 6. Thus, this case does not involve the failure of the neutral start switch to perform as intended. Rather, McMurray contended that Deere’s knowledge of the limitations of the neutral start switch made Deere liable for punitive damages. Punitive damages were warranted because Deere knew “that the neutral start switch would not prevent the engine from starting in gear if it was bypass started.” Id., accord rec. vol. I, doc. 15 at 2 (amendment to complaint for punitive damages). Yet the neutral start switch could not operate if the normal starting circuitry were bypassed. Rec. vol. I, doc 32, ¶ 1.6 at 2 (pretrial order). It was the tractor’s capability of starting in gear that was the claimed product defect in this case. See Plaintiff-Appellant’s Brief at 6. Accord rec. vol. I, doc. 1 at 5 (complaint); doc. 32, 111.8 at 2 (pretrial order). There simply is no evidence that the decedent *1446relied on the neutral start switch to protect him under these circumstances.
Regarding the claimed defect, the majority holds that the evidence was insufficient to instruct the jury concerning Deere’s defenses concerning 1) voluntary assumption of the risk of a known defect, and 2) abnormal use of the product. A party is entitled to instructions concerning its theory of the case if there is evidence, direct or circumstantial, to support that theory. Brownlow v. Aman, 740 F.2d 1476, 1489 (10th Cir.1984); Haines v. Powermatic Houdaille, Inc., 661 F.2d 94, 96 (8th Cir.1981). In deciding whether there is competent evidence to warrant the giving of an instruction, the inquiry is whether a jury properly could find evidence which would support a verdict based on the instruction. 9 C. Wright & A. Miller, Fed.Prac. & Proc. § 2524 (1971). In making this determination, a court is not to substitute its judgment for that of the trier of fact — it may not weigh the evidence or evaluate the credibility of witnesses. The evidence, and the inferences therefrom, are viewed in the light most favorable to the party seeking the instruction. Hallberg v. Brasher, 679 F.2d 751, 757 n. 6 (8th Cir.1982). More than a scintilla of evidence must support the requested instruction, but all of the evidence must be considered.
Applying this standard, I cannot agree with the majority’s conclusion that Deere was not entitled to an instruction on its assumption of the risk defense. The majority characterizes the evidence on this defense as purely speculative and conjectural. Majority Opinion at 1441. But if the evidence is viewed as a whole in the light most favorable to Deere, it is sufficient to support the, inference that the decedent was aware that the tractor could start in gear when shorting across the starter terminals. Merely because the decedent was unaware that the tractor was in gear at the time of the accident does not mean that he was unaware that the tractor had the capability to start in gear when bypass starting.
In deciding whether decedent had knowledge that the tractor could be bypass started in gear, the jury was entitled to consider the decedent’s familiarity with heavy equipment in general and this tractor in particular. The decedent was engaged in business as a contractor, specializing in large-scale earth moving operations, in several states. He had a considerable inventory of heavy equipment which was used in the business, including bulldozers, graders, scrapers, loaders, dump trucks and a tractor-trailer. Rec. vol. Ill at 186, 189-95, 196-198. Whenever decedent bought a piece of equipment, he would normally study the owner’s manual. Rec. vol. VIII at 42. His business employed up to eight heavy equipment operators, rec. vol. Ill at 238, but he also operated these pieces of equipment from time to time. Id. at 195. Decedent was an experienced heavy equipment operator,1 id. at 195, 232, and had considerable experience with this tractor, id. at 253.
On the issue of knowledge, the jury could also consider the operating instructions that decedent gave to others. Decedent owned two Deere industrial tractors. Rec. vol. VIII at 43. He had taught others to operate this tractor, including his wife and an employee. Rec. vol. VIII at 45, vol. Ill at 236. His wife testified that the decedent taught her to start the tractor with the key and with one foot on the clutch and one foot on the brake in the interest of safety. Rec. vol. VIII at 46, 48. He also taught her to put the tractor in neutral. Id. He taught his employee to put equipment in neutral for safety purposes. Rec. vol. Ill at 237.
On the issue of knowledge, the jury was entitled to consider why decedent might bypass start the tractor given the inherent danger of such a procedure. About the time of the accident, decedent was extremely anxious to complete the harvest because the crop had been planted late and decedent was completing another job in his *1447contracting business during the week, Rec. vol. VIII at 37.
The jury also could consider the way in which decedent operated the tractor. On previous occasions the tractor was bypass started with someone in the cab. Rec. vol. III at 239, 242-43. In fact, the day before the accident, the decedent trained his employee to operate the tractor. Id. at 245-46. The decedent bypass started the tractor on the ground while his employee was in the cab with the tractor in neutral and the clutch and brakes depressed. Id. at 242-43. The employee testified that he knew that the decedent was good about leaving heavy equipment in neutral, and this tractor had a decal in the cab telling the operator to put the machine in park and neutral before dismounting. Id. at 246, 249.
Taken together, these items are sufficient circumstantial evidence to entitle Deere to an instruction on assumption of the risk of a known defect. The testimony indicated that decedent was an experienced heavy equipment operator and very familiar with this tractor. Merely because he bypass started the tractor does not mean he was unaware of the risk. To the contrary, his willingness to bypass the starting circuitry may well be explained by the rush necessitated by a late harvest and personal time constraints. Placing someone else in the cab while bypass starting and placing the tractor in neutral are precautions taken to avoid runaway starts. The fact that decedent taught others to place the tractor in neutral is particularly significant because it is indicative of decedent’s knowledge that the tractor could start in gear. Finally, the decedent’s last words and actions support an inference of knowledge— once the engine started, decedent shoved his helper forward out of the path of the tractor and yelled “It’s in gear.” Rec. vol. IV at 34. Viewing the evidence in the light most favorable to Deere and considering all of the evidence, it seems to me the majority’s statement that there was no evidence whatsoever, direct or circumstantial, that decedent knew of the alleged defect in the tractor: that it could be started in gear,” is just plain wrong. See Majority Opinion at 1440. Reasonable persons could differ on whether the decedent was aware of the alleged defect, yet continued using the product; consequently, the assumption of the risk of a known defect defense was properly submitted to the jury. See Jordan v. General Motors Corp., 590 P.2d 193, 196 (Okla.1979) (“Where evidence is such that reasonable men might differ on the question of whether plaintiff’s awareness of defect and continued use of the vehicle was proximate cause of the accident, this defense is a question of fact for the jury.”).
The majority’s reliance on Smith v. FMC Corp., 754 F.2d 873 (10th Cir.1985), for the result achieved here is unpersuasive. In Smith, the decedents were killed when a piece of steel was dropped from a crane operating over their heads. Although the decedents were working on a job in the same general area where the crane was operating, they were working on a different job than the crane operator and there was an absence of evidence indicating that they were aware of any defect in the crane, let alone danger. Smith v. FMC Corp., 754 F.2d at 877. In this case the relationship between the decedent and the tractor is not attenuated, and there is sufficient evidence from which a trier of fact could conclude that either decedent was aware of the danger or could not have been unaware of it. See Rec. vol. I at 118-19 (assumption of the risk instruction); Bingham v. Hollingsworth Mfg. Co., 695 F.2d 445, 451 (10th Cir.1982) (instruction on assumption of the risk justified when there was “a risk of great magnitude which was obvious”).2
*1448The majority also holds that it was error to instruct the jury on the affirmative defense of use of the product for an abnormal purpose, a defense recognized in Oklahoma. See Fields v. Volkswagen of Amer-ica, Inc., 555 P.2d 48, 56-57 (Okla.1976). Essentially, the majority holds as a matter of law that bypassing the tractor’s starting circuitry would constitute, at most, use of the tractor in a careless manner (contributory negligence), not misuse or abnormal use of the product. Majority Opinion at 1443. Their analysis focuses exclusively on the intended end use of the product, no matter how improper an injured party’s attempt to use a product.3
At first blush, the majority’s analysis would seem to find support in Ford Motor Co. v. Matthews, 291 So.2d 169 (Miss.1974), a case cited with approval by the Oklahoma Supreme Court in Fields. In Matthews, the decedent attempted to start his tractor with the key while standing on the ground. The neutral safety switch, specifically designed to prevent the tractor from starting while in gear, failed and the tractor ran over the decedent and dragged him beneath the disk. Ford Motor Co. v. Matthews, 291 So.2d at 171. The defective aspect of the tractor was the safety switch itself; the plaintiff contended that a plunger connected with the safety switch failed, thereby allowing the tractor to start in gear. Id. According to the manufacturer, the decedent’s standing on the ground and starting the tractor while in gear constituted product misuse. The Mississippi Supreme Court rejected this defense because the “failure of the safety switch to prevent the tractor from cranking in gear was a cause of the accident.” Id. at 174. The decedent’s conduct was not “such misuse” as to relieve the manufacturer from strict liability. Id. The decedent, by inserting and turning the key in the ignition, did exactly what he would have done had he been seated on the tractor.
The facts of the case before us are different in one important respect. Here, the decedent did not use the key to start the tractor, he bypassed the starting circuitry entirely. Thus, we are not confronted with a situation where a neutral safety switch did not work as intended. Instead, the decedent used a completely different procedure to start the tractor, one which was not intended by the manufacturer. He was standing on the ground directly in the path of a giant tractor wheel using the shank of a screwdriver to short across the starter terminals. The introduction of a foreign instrumentality while deliberately bypassing the starting circuitry provided by the manufacturer at least creates a factual issue as to whether the aspect of the product at issue in this case, the starting system, was being used for an unintended purpose or in a way that could not be anticipated by the manufacturer. See Fields v. Volkswagen of America, Inc., 555 P.2d at 56. The majority recognizes that there is a factual issue as to whether Deere could foresee decedent’s manner of starting the tractor. Majority Opinion at 1443. But to hold, as a matter of law, that there can be no misuse of a tractor provided an injured party intends to use the tractor to plow fields, is simplistic and makes the manufacturer, who often cannot restrain the inventiveness of consumers, an insurer for virtually every accident that may occur. See n. 3, supra.
Likewise, the majority’s reliance on Spencer v. Nelson Sales Co., 620 P.2d 477, 482-83 (Okla.App.1980), is misplaced. The *1449defective product in Spencer was a suit of quilted long insulated underwear worn under the plaintiffs cotton overalls. Id. at 479. While the plaintiff was welding, a spark went beyond the overalls, igniting the underwear and injuring the plaintiff. Id. The defendant contended that the plaintiff misused the underwear by failing to wear leather overalls which would protect him from sparks. Id. at 482. The court of appeals rejected this contention, reasoning that, at most, the failure to wear leather overalls would be contributory negligence and that there was no evidence that the plaintiff was using the underwear for any purpose other than for warmth. Id. In the case before us, there is evidence that the decedent was not using the starting system provided by the manufacturer, but rather interposed his own starting procedure, which included the introduction of an instrumentality not provided by the manufacturer. In other words, the decedent actively altered the way in which the starter was supposed to be activated. This is not a case where the only possible factual determination is that the injured party merely used the product or used it in a careless manner.4
I would affirm the trial court’s judgment based on the jury’s verdict. In my view, the evidence entitled Deere to instructions concerning assumption of the risk of a known defect and product misuse. By insisting on more than circumstantial evidence to support these instructions, the majority has not reviewed the evidence in the light most favorable to triable claims and defenses.
. The majority apparently reads Bingham as requiring that there be direct evidence of plaintiffs knowledge of a known defect before an assumption of the risk instruction may be given. Majority Opinion at 1441 n. 5. While it is true that a trial court should submit an assumption of the risk "defense to the jury where the direct evidence of plaintiffs knowledge is unclear,” Bingham v. Hollingsworth Mfg. Co., 695 F.2d 445, 449 (10th Cir.1982), that cannot mean that knowledge of a defect may only be proven by direct evidence. Indeed, when the injured party is unavailable to testify, circumstantial evidence may be the only type of evidence available. *1448Moreover, there are certain products or procedures where the potential for danger is “readily apparent” and “obvious." Steele v. Daisy Mfg. Co., 743 P.2d 1107, 1109 (Okla.App.1987).
. Thus, were a party injured by attempting to start an older power lawn mower by turning the mower on its side and spinning the blade, an instruction concerning product misuse could not be given under the majority’s analysis if the party intended to use the mower to mow his lawn. In my view, such conduct transcends mere carelessness or negligence, which would not be a defense in a products liability action. Instead, like the instant case, the conduct is more accurately characterized as an abnormal use, one never intended by the manufacturer. Such conduct amounts to a gross deviation from the proper way to start a rotary lawnmower; it is a completely different procedure than what the manufacturer intended.
. The majority relies on a district court decision in Reed v. John Deere, 569 F.Supp. 371, 377 (M.D.La.1983), to bolster its legal conclusion that the decedent's starting method could not constitute use in an abnormal manner. Majority Opinion at 1443-44. The difficulty of using this case to support such a conclusion is manifest. First, the case involves a tractor which, after being key started and idling for several minutes, slipped into reverse, killing the plaintiff's decedent. Id. at 373. The "bypass" issue in that case involved whether the neutral safety switch had been bypassed, rather than repaired. Id. at 375. It did not involve an operator shorting across the starter terminals to activate the starter motor. In any event, the "bypass” issue was of no consequence because the trial judge found that the injury would have occurred whether or not the neutral start switch was working. Id. at 376. Even though the case turns on unreviewed factual findings, it may lend support to the notion that failure to start a tractor from the seat, when checking repairs, is not an abnormal use despite manufacturer’s warnings to the contrary. But it is an overstatement to say "But, as the court concluded in Reed v. John Deere, supra, the tractor was not used in an abnormal manner or in an unforseeable way when the decedent bypass started the tractor as he did." Majority Opinion at 1443.