When is a catch not a catch?
The rule book definition of a catch also lists situations that may look like a catch (to some), but in fact are not a catch:
If you "catch" the ball with a cap, any of your equipment (except the glove, of course), in the uniform pocket (go figure!), or any other part of the uniform, this is not a catch. In fact, it's an infraction that get's the batter a three-base award [ 5.06(b)(4)(B) ].
It is not a catch if immediately after securing the ball you collide with a player or a fence, or if you fall to the ground, and the ball is dislodged.
It is not a catch if a fielder touches a fly ball, then deflects it against a member of the offensive team or an umpire, and then is secured by himself or another defensive player. That said, if you touch a fly ball and deflect it directly to another fielder who then secures the ball, that is a catch.
It is not a catch if, on a third strike, a pitched ball strikes the umpire and is then caught by the catcher on the rebound.
It is not a catch if on a third strike a pitched ball lodges in the catcher's clothing or gear.