The Philadelphia Phillies chose Capel in the 24th round of the 1980 MLB draft, but the 18-year-old did not sign with the team; instead, he opted to attend the University of Texas.

He agreed to terms with the Brewers and played in MLB after an injury opened a spot on Milwaukee's roster, but was again released at the end of the season.

He spent the final part of his career in the Astros farm system, and after he made the 1992 Triple-A All-Star team, Capel played his last season in 1993.

[13] Capel played on the United States team in the 1982 Amateur World Series, overseen by the International Baseball Federation.

[15][16] The 1983 Longhorns finished the regular season with a 61–14 record and were ranked as the number one team in the nation by Collegiate Baseball Magazine.

[17] That season, the Texas team featured four future MLB pitchers: Capel, Clemens, Bruce Ruffin, and Schiraldi.

[12] As of 2018[update], his career winning percentage (.957) ties him with Rick Burley for the fifth-best in Texas Longhorns history (with a minimum of ten decisions).

[28][29][30] During winter, Capel, Greg Maddux, Manny Trillo, Damon Berryhill, and several other Cubs played for teams in the Caribbean.

[6] After the Cubs acquired Mike Bielecki from the Pittsburgh Pirates on March 31, 1988, they assigned Capel to Triple-A despite a Sun-Times prediction that he would be on the MLB roster.

[34] The Cubs recalled Capel and Mark Grace to the majors on May 3, while Drew Hall and Rolando Roomes were optioned to Iowa; at the time, he had a 1.54 ERA and two saves in Triple-A ball.

[36] On May 7, Capel made his MLB debut: he pitched the final 1+2⁄3 innings of a game against the San Francisco Giants, allowing no runs and no hits but issuing a walk in a 2–1 Cubs loss.

[37] His first career win came the following day against the Giants, although he blew a save by giving up a two-run home run to Bob Brenly and lost a 5–4 lead.

[38] Capel continued to pitch for the club until June 30, when the Cubs optioned him to Iowa to open a roster spot for Rich "Goose" Gossage to come off the 15-day disabled list (DL).

[49][50] When Greg Vaughn, returning from a turf toe injury and a sprained left ankle, was activated from the DL on June 11, Capel was sent to Triple-A.

Two days later, against the New York Mets, Capel allowed the game-winning home run to Howard Johnson in the top of the 11th inning.

[53] Against the Mets on June 14, Capel, starting pitcher Pete Harnisch, and closer Jim Clancy combined for a four-hitter.

[54] His final MLB appearance came on August 14 against the San Diego Padres, when he pitched one inning in relief of Jim Corsi in a 4–1 loss.

He told Javier Morales of the Arizona Daily Star "this [was] one of the greatest thrills of [his] career," and that he hoped it showed the Astros he could pitch in MLB.

[59] Capel elected to remain with the Astros organization where he allowed 26 earned runs in 32+2⁄3 innings and pitched the entire season in Triple-A.

[60] The Toros, managed by Rick Sweet, finished first in the Pacific Coast League (PCL) South Division with an 83–60 record and made the playoffs.

In the championship series, the Toros faced the Portland Beavers, champions of the North Division and holders of a PCL-best 87–56 record.

[69] Capel's son, Conner, played baseball as an outfielder for Seven Lakes High School in Katy, Texas, where he had a .456 batting average with 23 stolen bases and 36 runs scored in his senior year.