Real Dictionary

underperform
If someone underperforms in something such as a sports contest, or if one thing underperforms another thing, they do not perform as well as they could, or they perform less well than the other thing.

underperform in American English
to function less effectively or be less successful than expected or required
to perform less well than (another of its kind, a general average, etc.) or less well than expected
to produce a smaller return than

underperform in British English
verb: (of a stock or share) to yield a lower return than (the market as a whole)