Hello all, i wonder if anybody could help me, I have a 5 year border terrier bitch, she is lovely friendly with people and other dogs and is a joy to walk etc, that is until yesterday!!!

I was taking her on our usual walk with my daughter and we came across a minature schnauzer with a tennis ball in his mouth, the dogs said hello and all was fine then suddenly our dog just started going for the other dog, nothing awful happened but lots of snapping and snarling if you know what i mean. I managed to get my dog on her lead and then all was calm again.

Its now put me really on edge when I see other dogs coming our way, should i keep her on the lead avoid others or do you think it was just a one off. Don't really want to not let her say hello to other dogs as i imagine that doesn't help in the long run and usually she is very happy and plays with other dogs with no problems.
Could it have been to do with the tennis ball???
Any thoughts would be very appreciated,
Thanks x