mettlesome

adj

1. Marked by mettle or bravery; courageous.

   “The instant Haley touched the saddle, the mettlesome creature bounded from the earth with a sudden spring, that threw his master sprawling, some feet off, on the soft, dry turf.”

   “Among them was the "West Country" driver, Swain, of Bude, over the Great Central, who reminded me irresistibly of a hunter putting a particularly mettlesome steed at the fences.”