playground bully

uh oh!  I got in trouble today.  we went to the playground and  had fun running/playing with other dogs -   Then, I was playing ball with Gpa and very intent on the ball when 4 new dogs came running up behind me to play and surprised me and I turned on them with all teeth showing, growled  and took them all on.  Whoops!  they quickly left once I showed them I wasn't anyone to fool around with - Gpa wasn't very happy with me.  He was glad he didn't have to break up a fight that I almost started.   A little later 2 of the dogs returned with tails between their legs to try and play again - this time we played/had a great time and they knew I was the alpha dog (for now).  I just don't like to share my Gpa when we're playing and don't want to be messed with and I really don't like it when other dogs approach G&G and get attention.