Gerry Post plays the horses almost every night at local harness tracks, but even with his handicapping expertise, he couldn't figure out Towner's Big Guy, a pacer he owns.

The 2-year-old would race brilliantly one night, dismally another. He might qualify for a stakes race in sensational time, then look terrible in the final. Some horses mystify their owners and trainers in this fashion all their lives, but Post managed to learn the key to his colt.

When he did, Towner's Big Guy was transformed. The pacer has earned some $400,000 in the last few weeks, and he will be one of the strong contenders in tonight's Breeders Crown event at Rosecroft Raceway. With a purse of $673,533, it is the richest horse race ever run in Maryland.

Fourteen of the country's best 2-year-olds have come to Rosecroft for the race that probably will determine the champion of their age group.

They will compete in two heats (run as the seventh and eighth races), and eight of them will earn their way into the final, which will be the 11th race. The solid favorite is Barberry Spur, who paced a mile in a spectacular 1:54 1/5 when he won the $1.3 million Governor's Cup at Garden State in his last start. But he was only two lengths ahead of Towner's Big Guy in that race.

Gerry Post's colt has a plausible chance to pull an upset and offer further proof that a little guy can strike it rich in the standardbred sport.

Post has been an ardent harness fan for 30 years. He harbored the dream of owning a horse for a long time, but on his salary as a statistician for the Census Bureau he couldn't afford a major investment. In 1975, he and a friend went to a cheap yearling sale in Delaware and bought a colt for $5,700. "It turned out to be a real Cinderella story," Post said.

The colt, Big Towner, earned $547,000 in his racing career and was syndicated for $1 million when he went to stud. His success hastened Post's retirement from the government and enabled him to become a full-time horseplayer.

Post kept his involvement as an owner on a small scale -- he knew that lightning doesn't often strike twice in this business. But he said, "I decided I wanted one of Big Towner's foals." He and a partner, John Ostrander of Suitland, spent $67,000 at an auction for the colt who would drive them crazy during the early stages of his career.

Towner's Big Guy qualified for a stake at Garden State in impressive fashion, then finished last in the final. He qualified for the $2 million Woodrow Wilson at the Meadowlands, then got sick and had to miss the final.

"We knew he had some respiratory problems, and after that bad race at Garden State the vet suggested we might give him some allergy tests," Post said. "We sent him to the New Bolton Center, and they performed 31 tests on him -- the same kind of scratch tests they give to humans. He came up positive on three of them. He was so allergic to hay, straw and mold spores that he swelled up immediately in the tests.

"From that time on, we started bedding him down on peat moss and wood shavings. The vet started giving him regular allergy shots. And since that time every race has been super good."

In six races since his allergy treatments began, Towner's Big Guy has never been worse than second, and he comes to Rosecroft with earnings of $428,521. Realistically, Post acknowledges that Barberry Spur is the most probable winner of the Breeders Crown, but this is one time he hopes his handicapping judgment is wrong.