Rules Analysis
If a defensive player is guarding one offensive player and they are prevented from moving towards/with that player by another player, that defensive player may call "Pick". However it is not a pick if both the player being guarded and the obstructing player are making a play on the disc.
Note:
A pick should only be called if the obstructed player is within 3 metres of the player they were guarding at the time they were obstructed. However they do not need to be less than 3 metres away at the time of the call because the obstruction may cause this distance to quickly grow before the call can be made. Obstruction may result from contact with, or the need to avoid, the obstructing player. A pick cannot be called by the offense. After a pick the stall count should resume at maximum 6. A pick should not be called by a defender who was obstructed while attempting to make a play on the disc, that is not related to their ability to move towards/with the player they are guarding (ie they are poaching), however a defender may call a violation under Rule 12.7 if applicable. Extra: If the offence retains possession after an uncontested pick, the picked defender may go to the agreed place where they would have been without the obstruction. All other players, including the offensive player that the defender was guarding, should be located according to Rule 10.2. If the offence retains possession after a contested pick, all players, including the player who made the pick call, should be located according to Rule 10.2.
Prior to making the "Pick" call, the defender may delay the call up to two (2) seconds to determine if the obstruction will affect the play.
If the defender does delay the pick call according to 18.3.1.1, the pick is still deemed to have been called when it was actually called, and not when it occurred. If the defender waits longer then two seconds, 15.9 applies.