That performs less well than required.

present participle of underperform

To underachieve; to fail to reach standards or expectations, especially with respect to a financial investment.

plural of underperformance

The state or quality of underperforming

Third-person singular simple present indicative form of underperform

simple past tense and past participle of underperform

One who or that which underperforms, having performance that is below average or below expectations; often specifically a company or stock

plural of underperformer