Chaning obsession

I read the post on obsession with interest.  My son has become obsessed with WWE and I am fine with this obsession if it was harmless but as a result he wants to wrestle with everyone constantly.

He wrestes with himself on the trampoline and his toy Mario and that is harmless but when he starts to wrestle his 5 year old sister there are risks.

Any idea how we move him on to a new obsession which is safer for all involved?