One of the rather unusual rule changes adopted in the 2020 XFL season was picked up by the 2022 USFL: the double forward pass.
In the NFL and all other levels of football, a double pass may only be executed if one of the passes (usually the first one) is thrown backwards or parallel to the line of scrimmage. When the ball is passed backwards, the receiver is still entitled to throw a forward pass, provided he stays behind the line of scrimmage.
The USFL will allow two forward passes on the same down. The caveat is that the ball cannot cross the line of scrimmage at any point prior to the second pass. As long as both passes originate behind the line of scrimmage, and a player did not go beyond the line and retreat behind it, this is a legal play. So, for instance, a quarterback can throw a swing pass to a wideout and then sprint downfield to catch a pass from the receiver without having to call something complex like a Philly Special.
This also allows a quarterback, whose pass is batted back to him and caught, to throw a second forward pass right away.
The absolute limit is two, so even if the ball still remains behind the line of scrimmage, a third forward pass is not permitted. This will be penalized as 5 yards from the previous spot and a loss of down, consistent with the second-forward-pass penalty in the NFL. This penalty will also be assessed if the ball goes beyond and returns behind the line before the second forward pass.
If any forward pass is beyond the line of scrimmage — the passer’s entire body beyond the line of scrimmage at the point of release (which is reviewable) — the penalty is 5 yards from the spot of the pass and a loss of down. The play is not whistled dead on the illegal forward pass unless it hits the ground, which makes it incomplete.