Son maybe being bullied - what would you do?

Today at bedtime, my 5 year old tells me there's a kid at his school (not in his class, and either the same age or only a year or two older), who every day at recess, grabs his cap, runs away, causing my son to run after him, then throws the cap on the floor, at which point my kid retrieves it.He doesn't seem that upset by it. When I asked him if he cries he scoffed at me and I don't think he's at the point where he's making that up to protect my feelings. He said "But I always get my cap back, Mom," like that's the most important thing rather than the fact that some punk kid has decided that my son has been chosen as the source of his amusement (and in my mind's eye, probably his friends) every recess.It's a new school for him, in a new language. I'm worried. My husband thinks we should bring it up with the teacher. Is that too much? What would you say to him? I told him to tell the kid not to do that again, but I was at a loss after that. Tell the teacher? Punch the kid? I'm kidding.... via /r/Parenting http://ift.tt/2dme47n