#1 Nolan Ryan 301 strikeouts in the 1989 Seaon
Of course Nolan Ryan is number one on this list. 1989 was his first season in a Texas Rangers uniform after signing with the Rangers in the 1988 offseason. It was a much balley-hooed signing by the team that immediately generated a ton of fan interest and unforgettable moments. In that 1989 season Ryan was able to reach and surpass 5.000 strikeouts for his career. He is the only pitcher to have passed that 5,000 strikeout milestone in baseball history.
In 1989 the 42-year old Ryan was looking to continue his mark of leading the league in strikeouts much like he had done in 1987 and 1988 in the National League. He was looking to continue dominating that category in the American League. Ryan got off to a fast start as he struck out 15 Milwaukee Brewers in his second start and just kept going from there. He had double-digit strikeout games in 18 of his 32 starts.
Ryan ended the season with 301 strikeouts. He is the only Texas Rangers pitcher to have more than 300 in a season. He also won 16 games that season, had a 3.20 ERA, and pitched in 239 1/3rd innings. It was not so much a return to form as it was a continuation of his dominance at such an advanced age.
In 1991 Ryan made the All-Star team and finished 5th in Cy Young voting. It was a dominant run for Ryan that he was able to continue for another 4 seasons until 1993 when his elbow blew out and forced him into retirement at the age of 47 after an unbelievable run of 27 seasons. He was inducted into the Hall of Fame in 1999 with Robin Yount and George Brett in what is still one of the best Hall of Fame classes in the history of the sport.