Bit of childish fun agitating press barons, I finally assume (9,4)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

Anagram [agitating] of PRESS BARONS I {assum} E [finally]. A children’s game involving two teams, members of which chase and capture each other to increase the number of children in their own base. Another resort to aids here. I was going to say I never heard of it but it appeared once previously in a puzzle 15 years ago when I also didn’t know it.