OK guys calm down a little.
Yes flash is an issue but with sports photography you shoot what you can and as fast as you can. It's very rare to be able to get players to look in your direction. Only a change of position of the photographer can do that. BUT from the photo I can see it probably would have infringed on the play had he stood anywhere else. It's inside and the goals in 5-a-side or indoor tend to be against walls or have limited space.
I understand how you feel about the photo. It's a good one and I do like the composition and given the restricted access and position you had to be in it is an acceptable shot.
Only thing I will say is on the flash (as I said before) and the border. The border, for me, detracts from the image.
In the UK this isn't Law .. but it is strongly advised that you NEVER use flash around local/smaller clubs football grounds or indoors. And in fact I have seen photogs been requested by playing officials and by club officials to stop taking photos and leave the game.
Neophyte: My advice if you want it and this is only advice. For indoor crank up the ISO to 1600, open up to f/2.8 or there abouts, and got for it. But Outdoor is so much better. Try in the local games, kids games (get permission from parents etc. first).
Good luck.