All of the support class members are GODS of back hand slapping people. If Medic, Sniper, or Spy back-hand someone they'd have a mark on their face for weeks.
“Spy slappin’ my sentry!”
But no seriously, I love this idea. Medic has had to slap patients in and out of consciousness God knows how many times, so he’s perfected his slapping. Sniper has found that it works better on a lot of animals than punching them would, and so he’s turned to backhanding the rabid animals that attack him on his hunting trips. And Spy is a sassy little diva and he loves bitchslapping people to be dramatic, so of course he’s good at it.