THEME:   phrases starting with FOR but which could be read without FOR [most clever]   
GOOD ONES:     King's downfall   MATE [in chess; also at times in royalty]   
Balancing aid   EAR [I was sure it was BAR]   
Coat material   PAINT   
Boat propeller   OAR [oldie but goodie]      
BTW:   Excuse 
that last jeer?   FORGIVE A HOOT [lack of parallelism: the word "that" is definite, but "a" is indefinite]      
Discovered accidentally   
 LIT ON [Maybe found in some on-line glossary, but it's not in English… "hit upon" is the term.]         
RATING:    
 
  
 
Three grins = Loved it; Two grins = Enjoyed it; One grin = A bit bland for my taste; One teardrop = Not much fun