What happened: Tyler Mahle has a 1.48 ERA through five starts for Atlanta after carrying a 5.13 mark with San Francisco. Toronto and Tampa Bay follow Atlanta in the evaluation, while Houston is the only contender whose acquisitions and playoff outlook both declined.

Why it matters: Early returns have not tracked neatly with team performance: Philadelphia surged despite modest production from its new players, while Arizona's lone addition played well during a broader slide. That disconnect makes September results more consequential than the first month of individual samples.

What to watch: Arizona and San Diego remain neck and neck for the final NL playoff spot. The final month will show whether deadline additions hold up during the postseason chase.