Tennis is the easiest sport to lock focus on the player, there is no need for action priority. Same thing as Golf, and Cricket is much the same - so few players on such a big field.
How often are you shooting Tennis when there is a player in the background/foreground of the frame? It would only be doubles when from certain angles.
I have never shot American football, but I shoot Australian football and Rugby, and I have been told it could be the shape of the ball that would make that tricky. At times the camera might thing a player's head is the ball for example. Soccer, Basketball and Volleyball are all pretty simple when you think about it from the camera's perspective of identifying a ball.
And the same case applies to Hockey pucks, Cricket and Tennis balls. It could be hard for the camera to distinguish the ball from the background.