Can I use Not So Fast to counter Riposte?

Ruling: No, you cannot use Not So Fast to counter Riposte. Not So Fast can only counter spells or abilities that target units or gear friendly to you (the player of Not So Fast). Riposte targets a unit friendly to its own controller, not your units, so it does not meet the targeting requirement for Not So Fast.

Nuances:

• The term "friendly" is always relative to the controller of the spell or ability
• Not So Fast is designed to protect your own board state from opponent targeting
• Riposte does not interact with your board, so it cannot be countered by Not So Fast