Alpha A7IV configuring AF for basketball

[Alpino1912]

Hi all,

recently I've bought an A7IV, coming from a different system. I shoot with an FE 20-70/4 at the moment. Very easy, very light. My use of the camera is a family use, plus landscape ad basketball photography (my daughter plays on a local team). Not professional, passioned only. 

I'm experimenting some issues with the AF tracking in basketball photography. Sure for my inexperience. I'll try to explain.

The camera was set as follow: AF-C, face/eye detection on, flexible spot M /tracking, Af sensibility 1 (locked on).

I start focusing and tracking my daughter and everything works fine. As soon as another player appears between my daughter and me, the AF immediately (!) switches to this new player, losing the original subject tracked (my daughter).

I've read that the AF sensibility set to 1 (locked on) is tuned to stick to the subject selected and follow it, ignoring averything else.

Where am I wrong?

I can't understand..

Thanks in advace