Nappy horse

[Marmite]

Ill try to keep this short, I ride at a RS and one of the schoolies (whos normally reliable, safe, if a bit ploddy) has gone a bit strange. Just to clarify, back tack and teeth are all fine, this is an excellent RS, there isnt anything up with him.

He's being normal all the time except during a certain exercise, when he turns really nappy. When the ride are on a circle on the right rein, we do an exercise where each person trots to the top, canters a circle then back down to the ride.

He trots so far up the long side, fake spooks and trys to bomb it back to his mates. (I know the spooks are fake because I know the pony and his real spooks involve legging it forwards, not spinning round.) If you dont let him, he literally trots backwards. Dropping rein contact = legging it to friends. He does this over and over until he eventually gives up.

My question is, is there anythign else I could be doing? So far im using tonnes of inside leg coming up to the "scary" bit, tapping with a schooling whip too. As soon as he puts a foot wrong im getting more contact on him and more leg. If he runs backwards im legging him on and tapping him but still keeping a decent contact so he cant peg it to his friends. as soon as he's past the scary bit well, im praising him and taking the pressure off.

Anything else? When I tap he bucks, which doesnt bother me, im not scared of him at all, just schooling him out of it becuase he's meant for kiddies. He doesnt do it on any other exercise, or on the left rein, and you can do the circle at either end of the school and he'll still do it, hence why I think the spooks are fake.

Gonna get shot down for this, I can feel it but im starting to think maybe just one big smack might get him out of it? I really dont think theres anything wrong, he's just being nappy.