Merton had been reaching to pluck at the same hair, trying to figure out if it was blond or gray, so he could tease him about gray hairs. So he was a bit slow to realize he was about to get pounced.
Merton usually came out on the bottom in wrestling matches, since he tended to yelp and push more than actually counter attack. Which was what he did, though he did try to shove Heath off onto Gideon. "Gideon!" he called for help, trying to sound pathetic.