My point is that defenders don’t always have a chance to PI on down field throws. If they do the offense would gladly take 15 yards and a first down. Defensive holding is only 5 yards but why do you think defenders don’t do it so often? Wouldn’t you think if they were getting beat they would just hold on to the reciever? Giving an automatic first down is why.
They don't do it because it gets called even if the ball isn't thrown to them. Apples and Oranges.
Let me ask you, if you are covering a WR downfield (30+ Yards), and he has a step on you, and the throw is on target, you know that the WR has, what, a 90%+ chance of catching an on target pass, so you are going to let him catch it and get 30-40-50 yards and possibly a TD, or are you going to tackle him and only give up 15 yards?
100% chance of 15 yards, or
90% chance of 30, 40, 50 or more yards?
I know what I would do, and what DBs would do, and what D Coordinators would teach.
If you don't see the logic to that, I don't know what to tell you.