Following that season, he was signed by the Cardinals. He made his major league debut on April 17, 1902 at the age of 24. He was one of two power hitters on the team along with George Barclay. Many believe that if a rookie of the year award existed in 1902, Smoot would have been the winner. On April 25, 1902 he hit wo inside-the park home runs in one game. He had 510 at bats in his first season.
He managed to hit four of the eight home runs that the team had in 1903 and he had 500 at bats with a .296 batting average. His average dipped again in 1904 with a .281 mark in 520 at bats but he had 66 RBI’s, 23 doubles, 23 stolen bases and 37 walks in 520 at bats.
In his best year in a Cardinals uniform, he had four homers in 1905 along with 16 triples and scored 73 runs. He completed the season with a .311 batting average in 534 at bats.
1905 was perhaps Smoot’s best season. Not only did he tie his career high in home runs with four (which tied with Grady for the team lead), he also had career highs in runs (73) and triples (16). His .311 average, which also tied a career high, led the team and was seventh highest in the league.
1906 saw Smoot’s career got off on a rocky start as he was only hitting .248 with them. That prompted a midseason trade with the Reds, who sent Shad Barry in return for Smoot. After hitting only .252 combined that season, his major league career was over. He played his final major league game on October 7, 1906.
Smoot is the only player ever to have at least 500 at-bats in a season while playing in as many as five seasons. A .953 fielder, he hit .290 with 15 home runs and 269 RBI in his career.