He 'proved/showed his mettle' [=he proved/showed how tough he is] as a fighter tonight.
She'll have to be 'on her mettle' [=at her best] to win this competition.
The competition will 'test her mettle'.
(..) I'll be home before dark. - gunned down the marshal. He's now holed up in the mountains. You there. You look like the kind of man who'd put his mettle to it. What do you think, honey? Sounds fun. You're new. Not much of a rind on you. I'll give you a discount. No offense, but I'd rather - (..)2016 TvShow: Westworld Title: The Original Season: 1 Episode 1
(..) Murderous son of a bitch named Hector Escaton gunned down the marshal. He's holed up in the mountains. You there. You look like the kind of man who'd put his mettle to it. Not today, Sheriff. Apologies. Rye whiskey. What about it? Well, it ain't doing any good sitting in that bottle. You're new. (..)2016 TvShow: Westworld Title: The Original Season: 1 Episode 1