I was trying to remember something because I actually had a similar clause in a hiring agreement back when I used to work for a benefits administration firm. They had a stipulation that once I left employment I couldn't work for six months or so in any benefits call center environment. I wasn't sure of the legality of it, but I was told afterwards that in the state I lived in if the clause was an unreasonable restriction on my ability to earn a living, then it was not enforceable. It never came up after I quit, but there were plenty of people who worked there who immediately got similar employment elsewhere.
I do know that in California it would not be enforceable regardless of where it was signed. California doesn't recognize most non compete clauses and does not allow out of state non compete clauses to be enforced. So even if they signed this contract, they would immediately be able to work in California whether WWE liked it or not.