(S (S (S (BASENP (PRP He)) (VP (VBD estimated) (S (BASENP (PRP it)) (VP (TO to) (VP (VB be) (NP (BASENP (DT the) (NN length)) (PP (IN of) (QT (DQL ``) (QTC (BASENP (QP (NN three) (CC or) (NN four)) (NN football) (NNS fields)) (COMMA ,)) (DQR ''))))))))) (SBAR (IN though) (S (BASENP (PRP he)) (VP (VP (MD could) (RB not)) (VP (VP (VB be) (ADJP (RB entirely) (JJ sure))) (PP (JJ due) (PP (TO to) (BASENP (PRPD his) (NN vantage) (NN point))))))))) (PERIOD .))