Mostly (as I understand it) has to do with catching while going to the ground, whether it’s in the end zone, on the sideline, or in the middle of the field:
‘If a player goes to the ground in the act of catching a pass (with or without contact by an opponent) he must maintain complete and continuous control of the ball throughout the process of contacting the ground, whether in the field of play or in the end zone. This is also required for a player attempting to make a catch at the sideline and going to the ground out of bounds. If he loses control of the ball which then touches the ground before he regains control, it is not a catch. If he regains control inbounds prior to the ball touching the ground it is a catch.’
What I saw was our guy begin the process of the catch, but didn’t complete it. As they were going to the ground, the defender gained possession and maintained possession.
it could be argued that to overturn it you have to be sure the ball never contacted the ground, which I’m not sure there was a clear angle. Either way, I thought it was an interception in real time, and nothing about the replay changed my mind.