Below the mark and Second-string

Second-string and below the mark are semantically related in insignificant topic. In some cases you can use "Second-string" instead an adjective phrase "Below the mark", when it comes to topics like minor.

Second-string adjective - Being a replacement or substitute for a regular member of a team.

Below the mark and second-string are semantically related in insignificant topic. Sometimes you can use "Below the mark" instead an adjective phrase "Second-string", if it concerns topics such as minor.