Leg muscle cramping is a big issue for runners, and it particularly gets a lot of play in marathon and ultramarathon circles. When cramps hit, there’s really nothing you can do but walk. The traditional argument for the causes of cramping boils down to one or both of the following factors…
Source: Race Cramping: Causes and Prevention
We don’t know what cramping is, but we’re ruling things out.
It’s been months since I had leg cramps. It was in the pool, and I can’t remember why it would have occurred. I remember it being more frequent, for myself and others, when swimming after running. Most often, the cramps would be triggered by pushing off the wall when swimming laps. This is part of why I only do two of the three events (swimming, cycling, running) in a day.