1999 Penny Offcenter And Clamshell And Name Above We?

You might be focusing too hard on the superbowl. This isn't offside or even off center.

When only one side is not centered properly it is known as being struck by a misaligned die.

And this isn't a split planchet. The edge is showing signs of the blank planchet resting on the collar when it was struck. (a partial collar strike.).

Three dies are used for striking coins. Obverse, reverse, and collar dies.

Looks more like a railroad rim/partial collar to me than a clam shell. http://goccf.com/t/194814
http://goccf.com/t/345528
http://goccf.com/t/150245
http://goccf.com/t/164290
John1

On a clam shell it can be either a split planchet on the outside edge of the coin:

These are probably a thick lamination that is splitting off of the stock material. (It will not continue to split. The breakaway area is already seen. The rest of the metal is from the hot roll.
Or a split off cladding issue:


On these, some try to remove the cladding and think they will gain more money for them, but all the did was to reduce the value of that coin:

It would have been worth more as a clam shell. (The ghost strike shows that the cladding was removed)

Your coin is not that, but as mentioned a partial collar:

The area held in the collar is the normal width of the coin. Where the metal is not in the collar, it expands beyond as that area is not constricted with the collar. (Making it round and the reeds will not be on that area of the coin)

CoopHome : What is a partial collar error? How is it different from a clam shell coin? one is a planchet issue, the other is a striking issue.