Since order does not matter, you use the "n choose k" formula for unique combinations...
c=n!/(k!(n-k)!), n=number of elements to choose from, k=number of choices.
In this case n=9 and k=2 so
c=9!/(2!*7!)
c=36
There are 36 unique ways to pick 2 captains from 9 players.
