Yes, foul is a Scrabble word!
...and is worth 7 points in Scrabble, and 9 points in Words with Friends
foul
Verb
1. Hit a foul ball
2. Make impure
3. Become or cause to become obstructed
4. Commit a foul; break the rules
5. Spot, stain, or pollute
6. Make unclean
7. Become soiled and dirty
Adjective
1. Highly offensive; arousing aversion or disgust
2. Offensively malodorous
3. Violating accepted standards or rules
4. (of a baseball) not hit between the foul lines
5. (of a manuscript) defaced with changes
6. Characterized by obscenity
7. Disgustingly dirty; filled or smeared with offensive matter
8. Especially of a ship's lines etc
Noun
1. An act that violates the rules of a sport
What Scrabble words can I make with the letters in foul?
3 Letter Words
2 Letter Words