He earned the nickname "Mysterious" after pitching under a pseudonym for the San Francisco Seals of the Pacific Coast League in 1910.

The injury initially appeared not to be serious, but later that night Walker became "temporarily deranged" and, during his "delerium" he believed he was playing a football game against Northwestern that was scheduled for the following week.

[4] In November 1906, the Chicago Daily Tribune wrote: "Fred Walker is playing his third year on the maroon team and is considered to be one of the best all round players in the country.

"[5] Walker was also one of the most dependable pitchers for the Maroons' baseball teams for three years, also coached by Amos Alonzo Stagg, and won one varsity letter in basketball.

[4] In the summer of 1908, Walker played semi-professional baseball for the Rogers Parks team on the north side of Chicago.

In 1910, he coached the University of Mississippi baseball team and led them to the southern college championship, finishing with a record of 11–3.

[6][10] At the conclusion of the college baseball season in 1910, Walker left Mississippi and joined the Cincinnati Reds as a pitcher.

[11] Walker finished the 1910 season playing baseball for the San Francisco Seals in the Pacific Coast League.

He was the center of a throng as he left the stand and when he went to the offices of the baseball company, several hundred people gathered to look at him and call for a speech.

The press reported that Walker had signed earlier in the summer with the New York Giants but "got into trouble with a chambermaid at a hotel where he stopped, who accused the young pitcher of attempted assault.

"[16] Following the accusation, Walker had disappeared leaving no trace until his photograph appeared in the Los Angeles Times.

[18] In 1912, Walker signed with the Cleveland Indians and appeared in one game, pitching one inning and giving up no hits and no earned runs.

After pitching in the major leagues, he returned to Carnegie Tech as football coach in the fall of 1913, and played professional basketball that winter for Pittsburgh.

[11] During the fall of 1914, Walker served as an assistant football coach under Bob Folwell at Washington & Jefferson College.

[24] Walker served as the head football coach at Williams College in 1917 and led the team to the first undefeated season in the school's history with seven wins and one tie.

[27][28] After the basketball team lost the first 20 games of the season, the Dartmouth Athletic Council discontinued Walker's services in February 1918.

"[29] He signed with the St. Louis Cardinals in February 1918,[23] but spent the summer playing minor league baseball for the Newark Bears and Binghamton Bingoes.

[12] Following the United States' entry into World War I, Walker served as the athletic director for the Second Naval District at Newport, Rhode Island.

[36] In September 1920, Walker returned to the University of Chicago as an assistant football coach under Amos Alonzo Stagg.

[37] In February 1921, Walker signed a three-year contract to serve as the athletic director and head football, basketball and baseball coach at DePauw University in Greencastle, Indiana.

[42][43] In November 1924, Walker was hailed by the Chicago Daily Tribune as "Drury's miracle man" when he took "a team of light recruits" and developed them into one of the most sensational elevens in the history of the Missouri Conference.

[45] In his one year as the head basketball coach at Loyola, Walker led the team to a 12–6 record, including three wins over LSU.

He noted that he was dissatisfied with the ouster of the university president, James Oliver Buswell, and he intended to devote more time to his security business.