Jennings BABIP at .324, his .374w/OBA and .282 BA suggest that presently he is a slightly above average hitter against minor league pitching. His numbers are below several other hitters in the Durham squad in those areas. His impact may be more defensively but rest assured there will be a book on him(as there is on every other young player getting their first taste of big league experience) by the time he is called up. That book will be to see if he can handle anything other than a fastball. While it is a small sample, his contact ratio last year(when called up) of 63% on sliders and 83% on curve balls were well below his fastball contact rate. And his 0% BABIP on everything other than a fastball would be worrisome as well. He will be tested and there is a decent chance that he will not get consistent AB's under Maddon(and depending on what the Rays standings in the race is when he gets up) which may be the biggest factor in hurting a young player's success upon breaking in to the majors.