Board Thread:Questions and Answers/@comment-5767007-20140325061554/@comment-6053530-20140325091633

''Is Player A the turn player? ''

If yes, then Player A cannot respond. Player A must wait for Player B's spell to resolve first, then he/she may cast a new (counter) spell to start a new chain.

If no, then Player A may respond to the same counter chain, with Player A's spell resolving first, then Player B's.

Basically, when counters are activated, time freezes. Only when both players agree that there are no counter cards to be activated can the game proceed. Thus, you can start as many counter chains as you'd like, as long as you follow the correct order of resolution.