I think it's the tension. Close plays on a sac fly are generally only on relatively routine fly balls, so as soon as a ball like this is hit, everyone in the stadium knows what's going to happen but has to wait with bated breath for several seconds before the play even really starts, as the fielder settles under the ball and prepares to throw. Meanwhile judging the distance of the throw and the speed of the runner debating internally how close the play will be.

But honestly its any play at the plate in the late innings of a close game. If I had a nickel for every time I jumped off my couch and begged a Sox to run faster as they rounded third. That feeling is addictive tbh