Swimming: Cross-Training

Hi Everyone - My sport is primarily soccer and my training consists of aerobic endurance, interval training, and sprinting. Recently my hamstrings have been getting tight due to under use and over training of the quads. A friend suggested that swimming be added as a cross-training plan to find a little balance. Is there a general suggestion of what strokes are best for training the hammys? And any suggestions of what a good workout would consist of? Thanks in advance!