Denny Walling's journey through Major League Baseball is marked by his steady presence and adaptability on the field. Born on April 17, 1954, in Neptune Township, New Jersey, Walling attended Brookdale Community College before transferring to Clemson University, where he honed his skills as a baseball player. His talent caught the attention of the Oakland Athletics, who selected him in the first round of the 1975 Major League Baseball Draft.

Walling made his MLB debut with the Athletics later that year, but it was with the Houston Astros that he spent the majority of his career. Traded to the Astros in 1977, Walling quickly became a reliable player for the team. Known for his ability to play multiple positions, he primarily served as a first baseman and outfielder, though he also spent time at third base. This flexibility made him a valuable asset to the Astros' roster.

Throughout his tenure with the Astros, Walling was known for his consistent batting performance. He was particularly effective as a pinch hitter, a role in which he excelled due to his calm demeanor and strategic approach at the plate. His left-handed swing was a key component of the Astros' lineup, especially during crucial moments in games. Walling's batting average often hovered around the .270 mark, and he was known for his ability to drive in runs when needed.

One of Walling's standout seasons came in 1986, a year that saw the Astros reach the National League Championship Series. During this season, he posted a .312 batting average, contributing significantly to the team's success. Although the Astros fell short of reaching the World Series, Walling's performance was a highlight of the season.

In addition to his time with the Astros, Walling also played for the St. Louis Cardinals and the Texas Rangers. His stint with the Cardinals in 1988 was brief, but he returned to the Astros later that year, continuing to provide depth and experience to the team. Walling's final MLB season came in 1992 with the Rangers, after which he retired from playing professionally.

Following his playing career, Walling transitioned into coaching, bringing his wealth of experience and knowledge of the game to various teams. He served as a hitting coach for several MLB teams, including the Oakland Athletics, New York Mets, and Baltimore Orioles. His post-playing career in coaching further demonstrated his understanding of the game and his ability to mentor younger players.