arrived in the big leagues with St. Louis

[keannu]

1, What happened? Did he join St.Louis or join some other team to compete against St.Louis?
2. What do you think this "hop" means here?

mo3-37ex)There was an amazing pitcher whose name was Mordecai Brown. He was born in Nyesville, Indiana, in 1876. From the time he arrived in the big leagues with St. Louis, he was known as Three Finger Brown. Mordecai only had three fingers on his right hand, his pitching hand. That was the result of a farming accident when he was a youngster. But Mordecai gripped the ball the only way he could with his thumb and two remaining fingers. The result was a strange hop on the ball, one he probably couldn’t have achieved if his hand had not been injured. He played with five major league baseball clubs, and was famous for his exceptional curveball, which broke radically before reaching the plate. Mordecai Brown was eventually elected to baseball’s Hall of Fame in 1949, one year after he died.

[SoothingDave]

1. He joined the St. Louis baseball team.
2. His pitches had an unusual trajectory. They probably appeared to rise briefly, like they were hopping.