There have recently been a couple of incidents of people discharging their firearm in the holster, either while holstering or while drawing. This is a serious safety problem and is basically negligence on the part of the competitor for failing to engage the safety or disengaging it early.
USPSA rules require the handgun to have the safety engaged while holstering, i.e, placing the gun in the holster, and while holstered. The definition of holstering is placing the gun into the holster, not having it already in there and then engaging the safety. Still having your hand on it means nothing. The safety must be applied while placing the gun in the holster due to the very real chance that the trigger hangs up on something and the gun goes off. USPSA rules provide the following definition: Holstered—The point at which a handgun is inserted or engaged into the holster so as not to allow access to any portion of the interior of the trigger guard. Holstering begins when the handgun muzzle enters the holster or trigger guard enters block (for race gun holsters).
Conversely, the gun is drawn when the trigger guard/trigger is accessible. Draw—The point at which a handgun is removed or disengaged from the holster so as to allow access to any portion of the interior of the trigger guard. Disengaging the safety while the gun is in the holster as part of the draw stroke is extremely unsafe, as evidenced by a recent discharge in the holster attributed to the trigger being pressed by holster flex and the safety being disengaged in the initial grip. Not good. If anyone is teaching you to disengage the safety in the holster, get your money back and change instructors. There is plenty of time between drawing the gun and presenting it to the target to disengage the safety, and the gun should be pointed downrange when that happens.
Rules 8.5.2 and 10.5.11 describe the requirements, and it is a DQ to violate those rules, whether you’re holstering or drawing. Save yourself or others from being injured by an accidental discharge and play it safe.