The alarming stat that could sink the St. Louis Cardinals season

The St. Louis Cardinals have rebounded from a 15-24 start to the season and have the best record in the National League since Mother's Day. But just how good are they? Can they sustain their success and actually be a good team moving forward? When digging into the National League Wildcard standings, there may be more to the story, which doesn't bode well for St. Louis.

When scrolling to the right to look at each team's metrics on MLB.com, there's a major red flag for the Cardinals. Or, in this case, a red set of numbers: the Cardinals' run differential. After a crushing loss to the Reds in the series opener on Thursday, the Cardinals' run differential dropped to -38, lower than every team in the National League besides the Rockies and the Marlins, the only two teams with no real shot at playoff contention. When adding the American League, the Cardinals are above only the Blue Jays, White Sox, Angels, and Athletics.

So, how are the Cardinals the only team in this picture above the .500 mark with a playoff spot in hand? Firstly, their bullpen has been elite. Ryan Helsley has done nothing but dominate this season, adding to his franchise record with each save he notches. His supporting cast, including JoJo Romero, Andrew Kittredge, rule-5 pick Nick Robertson, John King, and others, have been stellar as well. However, the Cardinals bullpen is severely overworked. With Friday's call-up of Triple-A starting pitcher Gordon Graceffo and emergency usages of Adam Kloffenstein and Matthew Liberatore in the past, the bullpen could be at its breaking point.

With the Cardinals playing very few blowout games, the relief core is needed in high leverage nearly every night. While Sonny Gray, Kyle Gibson, Miles Mikolas, and to some extent, Lance Lynn have done a solid job eating innings and preserving the bullpen, the offense has done little to prevent the usage of the Cardinals' top relief arms. If the Cardinals could just score more runs in games where they could easily run away with a victory, they could preserve the bullpen to avoid an implosion.

Secondly, there is a bit of luck involved for teams outperforming their Pythagorean win-loss ratio. The bullpen has been a major help in winning close games, but the Cardinals may find their luck turning very soon. If they can't find a way to win games by a wider margin, some of the close games may turn the other way and St. Louis could find their inspiring run from 9 games under .500 squashed before the playoffs begin.