Berserkers of Blood Ridge

• WWizards of the Coast2010-08-15
  Official Ruling
  If, during your declare attackers step, Berserkers of Blood Ridge is tapped, is affected by a spell or ability that says it can’t attack, or is affected by “summoning sickness,” then it doesn’t attack. If there’s a cost associated with having Berserkers of Blood Ridge attack, you aren’t forced to pay that cost, so it doesn’t have to attack in that case either.

Rulings via Scryfall