You may discard this card after a Creature activates a Spell Upgrade within Range 1 - 3 in your forward arc. If you do so, the Creature's Spell Upgrade has no effect. All costs for activating the Spell Upgrade (Placing [Duration Tokens], disabling or discarding the Spell Upgrade, spending Target or Concentrate Tokens, etc.) remain spent, and the Creature's Action or attack is wasted.
After activating the Counterspell, you cannot attack for the rest of the round.