Plot hole: In the final tournament when Happy is stuck in the rough, he swings five times. Assuming he hit his drive into the rough and hit an AMAZING shot from the edge of the water into the hole, he still could do no better than a seven on the hole. Happy only lost one stroke on the hole. (01:16:50)
Plot hole: The bet between Happy and Shooter is in no way legally enforceable. Even if it was legal to make such a bet and it have it be enforced, the only person who can verify it was ever even made is Virginia who's obviously biased as Happy's girlfriend. The only way Shooter would actually honor the bet is to keep his word, which is completely out of character (he is the bad guy after all). And I'm sure with the money he's earned he can hire a bodyguard to protect him from Mr. Larson.
Plot hole: The bet between Happy and Shooter is prohibited, probably legally, but also definitely according to PGA regulations. It is prohibited for any professional athlete to gamble, on their sport in general and certainly on their own performance. Both of them could get suspended or banned from Pro Golf for this, and Shooter would certainly know it.