It does not matter how well "you" control "your" dog, there will always be others who insist on letting their untrained, unruly annoying little scruffball come over to you off lead and antagonise your dog.
My Alfie used to be great fun, playing with other dogs etc. however far too many offlead little sheits coming up to us in the local park has turned him into a devil dog when another is near (50-100m is near to him).
Poos sod has not been allowed off lead in the park for many years, except for when I take him into the caged ball court (ignoring the no dog signs) and have some ball play, which now it's winter will not be a lot.