Below par and Second-rate

Second-rate is a synonym for below par in below average topic. In some cases you can use "Second-rate" instead an adjective phrase "Below par", when it comes to topics like substandard.

Second-rate adjective - Of average to below average quality.

Below par is a synonym for second-rate in mediocre topic. You can use "Below par" instead an adjective phrase "Second-rate", if it concerns topics such as below average, substandard.