shī​cháng

abnormal

失常 shī​cháng
abnormal adjective
deviating from the normal state or behaving in an eccentric or mentally unbalanced manner

His behavior has become somewhat abnormal since he suffered the blow.

underperform adjective
failing to maintain one's usual standard of performance or level of skill

Due to excessive nervousness, the contestant underperformed in the finals.

Frequency

Movie subtitles
8.41 per million appears in 3% of films
Written text
7.80 per million

Sources

Definitions
CC-CEDICT