Tight End Covered/Uncovered

[OverAndBack]

Okay, we had this a couple times in a game I did yesterday, and I had to get the experienced guys on the crew to explain it to me. I thought I had it.

Now, I understand that what you see on Sunday has no bearing on what we do most of the time, but the Bears have been flagged twice for leaving their tight end uncovered.

Now, can someone explain to me what the deal is with covered/uncovered at our level, and if you know, can you explain to me why it's a penalty at the NFL level? I can sort of see if the tight end becomes ineligible by virtue of a receiver outside him, but they've called illegal formation and not ineligible downfield (which I would think would be the problem if a tight end becomes ineligible and he goes downfield).

Sorry, this is just one of those things confusing to the new guy.