There's no way around it: Golf is funny. The concept - hit a little ball with a skinny stick and try to get it into a tiny hole far, far away - is just plain ludicrous. And do this while not hitting the ball into sand traps, water hazards and your fellow golfers? Please. And then there's the clothing: bold plaids and loud colors are preferable. So it's no wonder that playwright Ken Ludwig opted to use the sport as the basis for his comedy "Fox on the Fairway," which Invisible Theatre opened Wednesday. ... Director Susan Claassen knows her comedy and she shaped a play that was easy with the laughs and polished enough to gloss over the script's rough spots. She had a cast that helped immensely.