When under attack, more often with multiple foes than single opponent combat, PC's can suffer a penalty when attempting to pick up a weapon they've taken from a foe.
As with the injury penalties, if you're lower extremities were too bdly damaged in battle, you, or your foe would have various degrees of difficulty when standing.
The same thing should hold true as well with being able to recover the disarmed weapon.
If the opponent were trying to pick up their weapon, and being under attack by multiple foes, they should be sometimes unable to pick up that weapon.
If we are unable to pick up the weapon when trying to do so while avoiding multiple attacks, why shouldn't they?
disarming penalties
Re: disarming penalties
There is already a chance for them to fail getting their weapon back.