General Spirit: Relievers are not infinitely available.
Overuse of pitchers will lead to declined performance and (for human-owned teams) severe injury.
SIM-owned teams are exempt from the injury penalty of over-use. However, they will experience the declined performance.
The reason for this is SIM-owned teams are being stewarded for human ownership. The more serious injuries on a team, the less appealing it is for a new owner.
Relief pitchers are defined by lower EN(durance) ratings, which dictate how many pitches they can throw per game. Typically, an EN rating below 73 denotes a pitcher who is considered a reliever.
There are three tiers of relievers:
There are four relief roles:
When you see a High-Usage warning on a reliever in your rotation it means he is out-pacing his innings-pitched limitation. The best course of action is to dial back his usage until is no longer out-pacing his limits.
When you see an Overused warning, it means your pitcher has exceeded his season limitation for innings-pitched. Any further pitching this season, including in the playoffs, will come with performance degradation AND high risk of serious injury.
As in real life, relief pitching needs to be monitored in the later half of the season. There are several strategies you can employ to help lower use for key relievers.
A summary of all these strategies could be: lean into cheap, low-quality innings eaters to save your best arms.
Pitchers you would normally never want on your team can be handy if used for a five game stretch here and there. Some of them will be predictably terrible, and some will over-perform. In either case, you might be able to get away with short stints from low-cost scrubs, or prospects who never really panned out.
Pitchers who are used as starting pitchers are able to extend beyond their relief inning limits, based on a ratio of game starts to overall appearances. This is especially handy if you have a starter who isn't good enough to crack your rotation, but can spot-start for you. The more a pitcher spot-starts, the more he can also be used as a reliever with a higher inning limit.
If you have an SR1 or SR2 pitcher who has a high-usage warning, it means they are out-pacing their IP limit of 50 for the season. However, a MR has a pace of 75, and a LR has a pace of 100. By switching the SR pitcher to MR or LR, you are extending their innings limit. (This does not change the EN-dictated pitch limit per appearance).
This might seem like a hack to circumvent the innings limitations. In reality the innings limitations are designed to reflect the wear and tear of warming up before each appearance. A pitcher who appears in more games for short-stints warms up more frequently, meaning he spends a higher ratio of pitches on warming up than on in-game pitching.
Deadline deals to bolster your bullpen for a stretch run and post-season is a great strategy. However, always review a reliever's current usage to ensure you aren't about to trade for a guy who is headed for declining performance and/or injury.