Random Semantics-related Question

So, let's say you're in a March Madness office pool:

Midway through the pool, you make a deal with somebody...."If I win, you get 10% of my winnings".

Let's say, entry to pool is $100, 1st place is $1000.

Do I owe him $100? or $90 (10% of (prize minus entry fee))?

How would you interpret it?

 

That's what I think. The entry fee is property of nobody once it's in the pool. "Profits" would obviously mean option B.