While we can clearly see that it was a rigged game, to the extent that this entire competition was honestly pointless if not detrimental to the narrative, I actually do see why he agreed to it. His basketball skills are not only very valuable to him but also a majority of his peers, girls included. To give jock senpai the benefit of the doubt that he's a character rather than a walking plot device, the third handicap is not something he'd have a problem with. If you look at his behaviors and motivations he pushed for this competition really hard less because he thought his crush was a trophy to be 'earned' and more because he wanted to make sure that seeing this really attractive (according to his peers) side of himself wouldn't change her mind.
His insistence of 'winning' her in a competition then in turn could be read as less as a purely misogynistic sentiment that a women's opinion doesn't matter and more the poor phrasing of an immature kid with limited emotional intelligence lamenting that she never got an opportunity to see his good and desirable traits before getting in a relationship and wishing for an opportunity to show them off in case that would change her mind. Sprinkle in a competitive drive and a touch of media of all kinds showcasing these kinds of competition, and the idea of 'winning' her in a competition is probably the only idea his mind could come up with to allow him to show off his skills in an environment where she might choose him instead. Once she demonstrates that this won't change her mind (via this third handicap), it's now clear to him that even if he confessed earlier she wouldn't have been interested in him so he should back off entirely. He's a teenager so this really isn't too outlandish, and ultimately would make the third handicap a non-issue for him as this competition is less trying to 'steal' her and more an extremely fumbled courtship attempt.
