From SSBA Knowledge Base

Hard Cap Amount

Starting in 2015: - $110 million Starting in 2018: - 2xCap ($87,600,000)

Penalty

Any time you acquire a player(s) (through draft, FA, or trade) that takes you over the hard cap, you lose your next available first round draft pick. This is a penalty for going over the cap. If you able to get under cap before the end of the current season (before contracts roll over to next year), you will not have to forfeit the pick. You cannot, however, trade your next draft pick while over the cap. If you do forfeit the pick, then I will pick a player whom I determine will not be drafted, and that player will be cut and become a free agent.

What Moves Can Be Made

You cannot make any moves while over the cap, unless that move results in a decrease in your team salary. The only moves that can add salary are the signing of minimum players prior to sim 1 that are needed only to give you 12 men on your roster, or signing a draft pick (outside of the one forfeited as described above).