Answer:
1/2
Explanation:
If you take 6 as your team then 3 of the 6 are forwards. That's 1/2 so your answer is 1/2. Note this answer uses the players already choosen on which position they play, but it is possible that a center could play either of the wings, and Right wing / Left wing could inter change with either wing or center. Then there is the possibility that all 6 players could play each other's position including goal.
If that last is case then the total number of ways is
6 * 5 * 4 * 3 * 2 * 1 = 120
The number of ways of choosing forwards is
6 Choose 3 = 6!/(3!3!) = 20
20 ways out of 120 = 1/6