This is a pretty strange play right here. Tracking down a sixth inning bomb from Jose Abreu, Red Sox center fielder Mookie Betts made the catch on the warning track. With his momentum taking him into the wall, Betts decided to leap over it and tumble into the bullpen rather than ram into the wall at full speed. Somewhere in the act of falling, however, Betts dropped the ball, and after a replay review the umpires awarded the two-run home run to Abreu.
From the MLB rule book (emphasis mine):
A catch is the act of a fielder in getting secure possession in his hand or glove of a ball in flight and firmly holding it; providing he does not use his cap, protector, pocket or any other part of his uniform in getting possession. It is not a catch, however, if simultaneously or immediately following his contact with the ball, he collides with a player, or with a wall, or if he falls down, and as a result of such collision or falling, drops the ball.
I can’t recall a similar play where a ball was caught several feet from the wall in the field of play, only to result in a home run after it was carried over the fence and dropped. Betts is a modern day Jose Canseco, I guess.