A shovel pass is when the Quarterback makes a short pass to the RB, WR or TE, that is moving through the pocket. He doesn’t throw it overhanded or underhanded, he pushes or flings/flicks it. Picture a 2nd baseman in baseball fielding the ball near 2nd base and flipping the ball to the shortstop so they can turn two. At times he’s pitching it a lot like an option QB does to the pitch man, but he’s pitching it forward.
In the play diagramed below, it’s 21 Shotgun Set (2RB 1 TE 2 WR) where one RB dives into the LOS, and the other is running the route to receive the shovel pass. The QB takes the snap (dotted white line) and looks down field, or dows a pump fake, and then flicks it (dotted purple line) to the back crossing in front of him. In this play, the RG (red line) is pulling and leading, and the LG (light blue line) is pulling and filling where he was was. The TE, X and Y receivers run routes that take the defender covering them away from the play and then block accordingly.
Here is an example of a version Denver used with Julius Thomas
Ignore the foreign team, but here is a great look at the flinging motion or the pushing of the ball forward.
It’s used often in the red zone/short yardage situations where the defense is expecting a pass but not a deceptive pass. Some would call it a trick play, but that is a stretch.
Some call it a shuffle pass, which is simply someone using an incorrect term.