WHERE DID MARK GET THE HANDBAND

There's a large possibility that it used to belonged to his grandfather. Remember how he found his grandfather's notebooks and a soccer ball when he was helping Atsuko cleaning up for New Year when he was a kid? Maybe he found it among his grandfather's soccer-related stuff too.

From club ._.
Because he is captain??

I think its his grand father's.

true captains never seem to show band for their leadership