Team A is in punt formation, seeing that they only have 10 men on the field they send a player in. The player is nearing or at 15 yards of the ball when the ball is snapped.

They had the legal number on the line. Is there a foul here?

NF

As long as the player had been within 15 yards and not offsides, then no. Unless you have an illegal shift , illegal motion, or some other penalty. As long as the player is close to 15 yards and it's in no way deceptive then I'll give him the benefit of the doubt.

So if Player A comes onto the field after his team has come set, there would be no problem?

If he comes onto the field prior to them coming set there would be an illegal shift issue?

How about if he is coming onto the field somewhere from behind the formation and is in a definite movement toward the LOS?

Thanks

After the final shift and before the snap, the entire team needs to be set. If the 11th player is still running to his position at the snap, we have an illegal shift because he never came set.

If the 11th player comes just onto the field, stops for a second, and then runs toward his position, we probably still have a flag for illegal procedure for not being within 15 yards of the ball. (Remotely possible that he's OK if the ball is on the near hash.)

If the guy runs to within 15 yards of the ball, stops for a second, and then continues to his position, and he's not moving towards the line at the snap, then we have legal motion and no flag. Even if he ran towards the LOS (before or after setting), as long as he's not going forward at the snap, he's ok.