I get it all the time, not just during sport, it is worsened with exercise though because I heat up during exercise, which triggers a fake/pseudo-exacerbation (a temporary worsening of symptoms) in many people with MS. Even a half a degree rise in body temperature can cause this for some where for others it may require a greater rise, it is referred to as Uhthoff's Phenomenon (or Uhthoff Phenomenon).
For some, hot weather can do it, as can hot showers, hot tubs, etc.