I've never had problems in the races I've done, but they were all wave starts, not mass start. So you only have 200 people together at a time, not 2000. Makes a big difference. I've heard the mass starts can get a little ugly. I've gotten knocked a few times, but it's usually just when I catch up to the poor swimmers in the wave ahead....I feel like drowning people that do breast stroke and end up kicking me in the ribs.