Walling began his professional career as an outfielder. Just three months after being drafted by the A's, and before he appeared in a game in the minor leagues, Walling made his major league debut on September 7, 1975. He appeared in six games for Oakland down the stretch, getting one hit in eight at bats for a batting average of.125. Walling opened the next season in the minors with the Chattanooga Lookouts, the A's Class-AA affiliate. After batting.257 in 115 games for Chattanooga, Walling was again in Oakland in September. This time, he played just three games, going 3-for-11 for a.273 average. In, Walling was back in the minors to start the year, but played just three games for the Class-AAA San Jose Missions in the first two months due to injuries. On June 15, Walling was traded to the Houston Astros for outfielder Willie Crawford, who was playing his last season in the majors after a long career.
Houston
After being traded to the Astros, Walling was assigned to Class-AAA Charleston Charlies. He played 29 games for Charleston and batted.348. It would be the last time Walling played in the minor leagues for over a decade. He was once again promoted to the majors in September, this time playing in six games, going 6-for-21 with 6 RBI. In, Walling was the closest thing the Astros had to a regular left fielder, playing 49 games there, more than anyone else on the team. However, even then, he made more appearances as a pinch hitter than in the field, as he played only 55 of his 120 games as an outfielder. The Astrodome was a notoriously difficult place to be a batter, but Walling managed to be about an average major league hitter, posting an OPS+ of exactly 100. Overall, Walling batted.251 for the Astros, with 36 RBI. Over the next ten seasons, Walling played much the same role on the Astros, generally playing only against right-handed pitchers. For his career, Walling batted seven times as often against righties as against left-handed pitchers, prompted perhaps by his significantly lower batting average and slugging percentage. Statistically, his best year was, when he set career highs in several categories, most notably in home runs and RBI while batting.312 in 130 games. During this time, he shifted all over the field, playing good chunks of time at first base in, and, while playing mostly third base from until, when he was traded to the St. Louis Cardinals on August 31 for pitcherBob Forsch.
Cardinals
Walling played two and a half seasons in St. Louis, mostly as a pinch hitter. While he batted.304 in in 79 at bats, he batted just.220 in, and was allowed to become a free agent at the end of the season.
End of career
Going into, Walling signed with the Texas Rangers. However, he went just 4-for-44 in 27 games, for a batting average of just.091. He had just one double and three singles among his hits, and had just 2 RBI. He was released by the Rangers in June, and did not play professionally for the rest of the season. In, Walling briefly attempted a comeback with his longtime team, the Houston Astros. However, he batted just three times with one hit before retiring.
Coaching career
After his playing career ended, Walling remained in baseball as a coach. In the major leagues, he has served as the hitting coach for the Athletics from until, and for the New York Mets from until. In both positions, he served under managerArt Howe, who was his teammate in Houston. In, he was hired by the Orioles as their roving minor league instructor and later became the hitting coach for the Norfolk Tides.
