His AVG-OBP-SLG in Sept were .269-.315-.420. Those numbers are a bit of a surprise and a bit of a disappointment for the Angels given that he was over 1.000 in OPS in July and August and had .977 in June. The table below shows his OPS+ for each month of his career.
At 104, his OPS+ is far below the next lowest ever for Sept (actually Sept/Oct). The next lowest was 143. It also looks like his 3rd lowest monthly OPS+ ever no matter what the month. In 8 of his 11 previous seasons, his Sept OPS+ was higher than what it was for the whole season. His worst differential had been -17 in 2003. Yet this year it was -37. So his Sept performance was very much out of character. Maybe a normal performance would not have helped the Angels as they finished 4 games out of the wild card.