You know your four year old doesn't need to watch UFC when . . .
I don't really care what people let their kids watch, what video games their kids play, that sort of thing. The media your children enjoy is not nearly as important as having a parent there to help understand what's real and what's not, what's acceptable behavior and what's not.
Having said that, there is a point sometimes when you are given an example that perhaps your child isn't getting the parental input they need. And perhaps The Boy doesn't need to watch mixed martial arts fights. The sign was simple enough to read in glaring neon.
So, you know your four year old doesn't need to watch UFC when you're lying on the couch and he comes over because you tricked him into coming close enough for you to drag him onto the sofa for tickling and giggling and instead of all that, what you get is the hammer fist. Yes, my four year old tried to pull out the ol' ground and pound. It sucked more for him because if he's going for the hammer fist it's only natural that I get him in the guillotine and choke his little ass out.
Disclaimer: My son did not in fact actually attack me. He did, in a playing way, use the hammer fist just as he has seen done. I in fact did not choke him out nor did I use any other submission on him. The only submissions I use on my children involve the fact that I'm enough bigger to force access to their belly for tickling.