Cardinals DB Tyrann Mathieu confirms that Travis Kelce is off the chain

I don't know the context behind this tweet from Cardinals DB Tyrann Mathieu ...

Travis Kelce is off the chain.

— Tyrann Mathieu (@Mathieu_Era) March 17, 2015

...but it could mean so many different things. Mathieu could be talking about Kelce's:

• Game tape
• Blocking ability
• Dance moves
• Obscene gestures
• Twitter game

What else could he be talking about?