What does the term "tighten up" mean?

Question

Although I've been a horse player for ten years, I've never understood what my fellow gamblers meant when they yell "tighten up, Prado!"

Usually "tighten up, Castellano!" is yelled as the horses enter the stretch run. What are they urging the jockey to do?

Answer 1

Race horses react to the length of the rein.  When they go along in the early part of the race, the jockey lets them move at their pace with a longer rein.  When the jockey asks the horse to open up his stride and run faster, he'll shorten the reins (or tighten them).  When the gamblers yell for the jockey to tighten up, they're rooting for their horse...  they want the jockey to make his move now.  Tighten up on the reins so the horse will open up his stride and go faster so he'll go up to the lead and win the race.