Now that does describe my oldest horse. So
competitive, he nearly pulled over the trailer he was tied to (with his buddy)
at lunch during a Competitive Trail Ride when he noticed that horses were
beginning to leave camp at a walk to start the afternoon section of the
ride.
Now, his main issue is competitiveness. He is not herd-bound at
all. He will leave the other horses in a blink. He is (now) calm in
camp, even during warmup before the ride. He is calm when walking out of
camp, if he is not in a group. Calm when he is traveling by himself.
He melts down when he sees the first horse ahead of him, or when caught
in a group, and has been known to try and block the trail to prevent a horse
passing him (he got corrected.) Once back at camp, he will settle down
again.