Is this sexual assault??? Help me.

So I’m in color guard at my school (the people that twirl flags with the marching band). So we’re currently in our indoor season and we were practicing a dance-oriented part of our show in the band hall where there is limited space. (I’m a freshman and 14 btw) my “mentor” for the year (who is 18 and a senior) accidentally (I think) tripped on my foot due to the limited space. He grabbed my shoulders as you would have expected to try and balance himself but he didn’t stop there. He continued to move his hands around my body, onto my hips and love handles as well as managing to get behind me and hug me from behind. This isn’t the first time something like this has happened. Anytime he goes to give me a hug his hands either end up in the small of my back or lower or on my hips. He’s also come up and hugged me from behind and when we went out to eat as a team he sat next to me and kept pressing his thigh against mine even though I kept moving away. Is this sexual assault or am I just over reacting? I really don’t know what to do. I’ve told a few of my friends about it and a few people saw what he did in the band hall but I don’t think my coach did. Please tell me what to do or upvote this so more people see it.

UPDATE: I don’t want to answer comments so I stay anonymous. Yes this makes me uncomfortable and I’ve asked him to back off once or twice but I’m really scared to say anything else... there are already rumors about us going around and more drama is the last thing I want right now.