What's the meaning

of put 5 in the back?

"In HS, I partook in an exchange program that involved me living with a French family in Paris for a month. Anyways, they had a kid who was ~1 year younger than me (so 16 or so) who was obsessed with Pro Evolution Soccer for PS2 (game similar to FIFA). I sucked at video games or anything but I eventually obliged in playing a few games with him. He pwned me pretty thoroughly and decided he wanted to see if he could beat me 5-0 and we would bet 5 Euros on this. I refused but he kept nagging so eventually I obliged. I obv. played with Chelsea and put 5 in the back and he only won 2-0."

Thanks a million!