You had to show your mettle on the pitch, and only then would he open up.
With all you fit young men a doctor doesn't have much of a chance to show his mettle.
As for the politicians; at times like this it is that they show their mettle.
On the face of it, he showed his mettle in the boxing ring.
It was then that the stooped man showed his mettle.
With or without him, though, Carroll will have to show her mettle, in every sense of the word.
All of them had shown their mettle in previous engagements.
Steer will have to show its mettle to win contracts.
But he showed his mettle and now we love him.
"However, you and I must do some practicing so we'll show them our mettle."
Idiome