What would you do here?

Ok so 2 weeks ago at my high school baseball game I found a $50 dollar bill in the dugout. Almost the whole team saw me pick it up so I couldn't hide it. When they saw I had it they said it might be my coach's money. It turned out it wasn't his but he took to see if anyone from that school district we were playing would claim it. Earlier today, he gave it back and said nobody claimed it. However, when I got to homeroom in school, my friend said that it was his money that his mom gave him for gas. I didn't say anything right away, because I didn't know what to say. He then asked "well are you going to give me my 50 bucks?" I kind of hesitated and just said I didn't know. I told him if he brought in 25 bucks tomorrow I would hand him the 50 and take his 25 so we could split it. The thing is,something is fishy about this. If it was his money, why would he wait 2 weeks until I finally got it to claim it. He's my friend and all, but this seems odd if you ask me. I'm definatley not giving him the whole 50 dollars back. I found it, and he had his chance to claim it and he didn't. But should I even give him any amount back at all. I asked a few people what to do and they said they wouldn't give any to him. I don't know what to do. My one friend told me to talk to my coach or principle about it. What would you do in this situation?