As we approach the quarter pole of the regular season, the Yankees have fallen back to .500 and the middle of the pack in the AL East. They've lost 4 in a row and 9 of 13, leaving them with a 19-19 record and a -18 run differential that is 3rd worst in the AL behind the Astros and the Rangers. A few weeks ago, when they were playing better baseball and winning, the negative run differential was downplayed because of the small sample size of games. Now that the sample has grown, a split of those 38 games shows a disturbing trend:
First 19 Games: 11-8 Record, 75 Runs Scored/84 Runs Allowed (-9 differential)
Last 19 Games: 8-11 Record, 94 Runs Scored/103 Runs Allowed (-9 differential)
Based on that split, the Yankees have basically played the same brand of baseball since Opening Day. They've scored more runs and given up more runs over the last 19 games, but it's basically been below-average baseball and that's reflected in the matching run differentials. They outplayed their run differential in the first 19 games and won a few games more than they should have and they weren't able to do that over the last 19 games, which is why they are where they are with a .500 record.
If luck wasn't on their side in the first 19, we'd probably be looking at a 17-21 team that's perfectly in line with its Pythagorean-expected record. Considering all the injuries that have happened in the last 19, that doesn't exactly bode well for the future.