Some pitchers (Mariano Rivera most prominently) throw what's called a "cut fastball", which has a signficantly higher than average tendency to break the bats of hitters. My question is: why? It's the same ball, the same bat. The velocity on the ball is no higher than other pitches which do not have that tendency. I presume that it has something to do with the spin that's imparted on the ball, but I have no idea why that would work that way. What gives?