off-season; out of season
Refers to produce, seafood, or other seasonal items that are not at their peak season. Can also describe timing that is not ideal for a particular activity.
旬外れの野菜は味が落ちることがある。
Off-season vegetables can sometimes lack flavor.
この魚は旬外れなので、あまり美味しくない。
This fish is out of season, so it's not very tasty.
Formed from 旬, “the proper or peak season,” and 外れ, “being outside or missing,” hence “out of season.”