Yes, sass is a Scrabble word!
...and is worth 4 points in Scrabble, and 4 points in Words with Friends
sass
Verb
1. Answer back in an impudent or insolent manner;
Noun
1. An impudent or insolent rejoinder
2. A specialist regiment of the British army that is trained in commando techniques of warfare and used in clandestine operations (especially against terrorist groups)
What Scrabble words can I make with the letters in sass?
3 Letter Words
2 Letter Words