When my hamstring injury flares, the pain refers down the side of my leg and that's actually what bothers me the most. It almost mimics sciatica in that sense. The massage ball I use is from a company called Trigger Point Therapy, but any hard ball will do. I keep a tennis ball in my car and at my office. I hadn't thought of a lacrosse ball.

I've been living with this for some time, and have kept it pretty well under control with some massage after my initial round of PT. I do a lot of exercises to strengthen the hamstring, too. Bridges are one of the most effective, along with some balance poses. My PT warned me that it could take a very long time to heal and that it might long bother me. So I would suggest that you incorporate some massage on a regular basis, even if it stops hurting.