A fly ball hit a batter's helmet and was caught on the rebound by a fielder, resulting in an eventual out call from the umpires, but not for the catch. Let's look at the interference rule to figure out what happened, and we'll look at both college and professional baseball rules because they are nearly identical for this play, which occured in the Pacific Empire League, a first-year collegiate summer league.
First, we refer to rules like NCAA 6-2-a or OBR 5.06(c)(5) which state the ball becomes dead when "
A foul ball is not caught, in which case runners return to their bases."
For the issue of a catch in this situation, see NCAA 2-16: "It is not a catch if a fielder touches a fly ball that then hits a member of the offensive team or an umpire and then is caught by that fielder or another defensive player."
Accordingly, an air out for a catch is an incorrect ruling.
Instead, we must consider fair/foul, as in NCAA 7-11-1: "A batter is out when a batted fair ball touches the batter-runner outside of the batter’s legal position in the batter's box before touching a fielder."
But if the ball is foul, we must consult the interference rule for right-of-way going to a fielder on a batted ball, as in OBR 6.01(a)(10): "It is interference by a batter or a runner when they fail to avoid a fielder who is attempting to field a batted ball, or intentionally interferes with a thrown ball."
Accordingly, the most realistic outcome here is the umpire ruled the batter-runner interfered with the catcher by failing to avoid the fielder attempting to play a batted ball. I disagree, but rules-wise, that's the only call that seems to be supported by the book. Absent interference, this is a foul ball.
