If you use the web based game launcher battlelog it will give a detailed explanation for kick or ban - if the only msg you received was 'kicked by admin' then this is the games default msg and you weren't kicked by an in-game admin.
Several reasons this may have happened:
VPN kicker - ensure you are not using a VPN
Ping limiter: ifyour ping is too high you will be auto kicked
Punkbuster: make sure your punkbuster is up to date
VIP: the game will kick at random any non VIP player to accommodate for a VIP member if the server is full
Outside all of this, you can always fill this form out and we'll look further into it on our end