The Supplemental is held for the players who apply BECAUSE they lost college eligibility in between the deadline to register for the REGULAR draft and the deadline to register for the SUPPLEMENTAL draft.
What Sorsby's lawyer is saying is that the NFL is unreasonably (and against the collectively-bargained guidelines) withholding permission to enter the Supplemental.
In Sorsby's favor:
1. The application was timely
2. The eligibility reason is accurate
In the NFL's favor:
1. Apparently Sorsby did not provide any supporting documentation that explained his eligible reason
2. The NFL has no obligation to keep pushing back the deadline, just because one guy and his attorney couldn't get their **** together
To sum it up in some terms that the lawyers will understand, the NFL needs some time to examine the supporting documentation, particularly the issue that the NFL raised, which is that the lawsuit against the NCAA was "recently dismissed". As many of us know, a lawsuit can sometimes be voluntarily withdrawn in order for the plaintiff to amend and refile. However, if the lawsuit was dismissed or withdrawn with prejudice, it is nearly impossible to refile. What the NFL is "trying to avoid" is that they let Sorsby into the Supplemental, then he refiles his TRO and finds that same-old same-old corrupt judge who grants his TRO, and now you have a guy "in the draft" AND ALSO with remaining college eligibility.
The NFL doesn't want another NBA "Charles Bediako" situation.