As he stepped across the threshold, Tommy brought the picture down with terrific force on his head.
( ( As ( he ( stepped ( across ( the threshold ) ) ) ) ) ( , ( Tommy ( ( ( brought ( ( ( the picture ) down ) ( with ( terrific force ) ) ) ) ( on ( his head ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (NP (PRP he)) (VP (VBD stepped) (PP (IN across) (NP (DT the) (NN threshold)))))) (, ,) (NP (NNP Tommy)) (VP (VBD brought) (PP (ADVP (NP (DT the) (NN picture)) (RB down)) (IN with) (NP (JJ terrific) (NN force))) (PP (IN on) (NP (PRP$ his) (NN head)))) (. .)))
Tommy hurt his head bringing the picture down.
( Tommy ( ( ( hurt ( his head ) ) ( ( bringing ( the picture ) ) down ) ) . ) )
(ROOT (S (NP (NNP Tommy)) (VP (VBD hurt) (NP (PRP$ his) (NN head)) (S (VP (VBG bringing) (NP (DT the) (NN picture)) (PRT (RP down))))) (. .)))