Counter target spell. Its controller can't cast spells this turn.
4/15/2013 You must be able to target a spell to cast Render Silent.
4/15/2013 Render Silent doesn’t stop any player from casting spells in response to Render Silent before it resolves.
4/15/2013 The affected player can still activate abilities, including abilities of cards in their hand (such as bloodrush abilities), and the player can still play lands.
4/15/2013 If the spell is an illegal target when Render Silent tries to resolve (because it’s been countered by another spell, for example), Render Silent won’t resolve and none of its effects will happen.
4/15/2013 A spell that “can’t be countered” is a legal target for Render Silent. The spell won’t be countered when Render Silent resolves, but that spell’s controller won’t be able to cast spells for the rest of the turn.