I played tennis till I was nearly 6mths pg and was unable to move quick enough to get the ball. Everyone has their own comfort level when it comes to playing sport in pg - I have knee-boarded till 8mths and played netball till 13wks as well (only stopped because the comp finished).

Don't forget that till 12wks the baby is nicely hidden in behind the pubic bone so if you get hit with a ball it wont hurt anything.