throw elbows when necessary 
(ROOT (S (VP (VB throw) (NP (NNS elbows)) (SBAR (WHADVP (WRB when)) (FRAG (ADJP (JJ necessary)))))))
(ROOT (S (VP (VB ) (NP (NNS )) (SBAR (WHADVP (WRB )) (FRAG (ADJP (JJ )))))))