A detailed graphical explanation of the SportsSystem codes can be found here.
Some examples of the more common codes for being disqualified are listed below:
DQ ST - Moving at the Start.
Under the ASA Technical Rules of Racing (SW 4.4) any swimmer starting before the start signal has been given, shall be disqualified. If the starting signal sounds before the disqualification is declared, the race shall continue and the swimmer or swimmers shall be disqualified upon completion of the race, if the disqualification is declared before the starting signal, the signal shall not be given, but the remaining swimmers shall be called back and start again.
DQ T- Did not touch simultaneous at turn or finish.
In Breaststroke a common cause of disqualification is if a competitor touches the wall with just one hand during the turn. Under the ASA Technical Rules of Racing (SW 7.6) at each turn and at the finish of the race, the touch shall be made with both hands simultaneously at, above, or below the water level.
In Butterfly, ASA Technical Rules of Racing (SW 8.4) at each turn and at the finish of the race, the touch shall be made with both hands simultaneously, at, above or below the water surface.
DQ-O - Swimmer #2 started before swimmer #1 touched.
Relay changeovers are valid when the feet of the outgoing swimmer detach from the board at least 3/100 seconds after the fingers of the incoming swimmer touch the wall. If the outgoing swimmer moves too early, their team is disqualified.
DQ-SH A 3L - Stroke - Head, Appeal made, 3rd Length
For example in Breaststroke ASA Technical Rules of Racing (SW 7.4) states that during each complete cycle, some part of the swimmer's head shall break the surface of the water.