Push off on time
Many swimmers of all ages push off the wall to begin a swim by either pushing off early, so they can beat the person next to them or get a fast time, or by pushing off too late.
For those leaving early, you are only cheating yourself and the time you get is not a real time. If you push off late it is normally because you are not 100% focused.
The majority of swimming pools either have digital clocks or round clocks that swimmers can use to push off at the right time. Make sure you always start a swim on the right time.