To win, you wager more than the opponent. The CPU is really good at initiating a clash when they have 1 more bar than you, and then wagering that much. You click the button corresponding to the amount you want to wager.
"Gary was here. Ash is a loser!" = Greatest Tramp Stamp Ever
I have never initiated a wager (I dont know how!) But the computer does not only do it when they know they can win because as long as you conserve bar correctly you should have more than them in the second round (when they usually use it for health)
p.s. this is what the alphabet would look like if q and r where removed~ Mitch Hedberg R.I.P