Mark was a powerful righthanded pitcher in the Mon-Clair League for 20 years. During that span, he won four ERA titles, nine division championships and six Valmeyer Fourth of July tournaments with the Waterloo Buds, Waterloo Millers, Belleville Rockies and Fairview Heights Redbirds. His first ERA titles came in 2009 and 2011, the latter season posting a 2.40 ERA. In 2013, he helped the Millers win the Mon-Clair League championship, with Mueller twirling a brilliant one-hit shutout in Game 3 of the playoffs. He pitched the next two seasons for Belleville and in 2015, he won his third Mon-Clair ERA title with a 3.13 mark. His final ERA title came in 2019 when he posted a sterling 1.36 ERA. Mueller played baseball in Australia for three years and had a no-hitter for the Woodville Senators. In 2004, he pitched in the Frontier League for the Gateway Grizzlies – where he was in the starting rotation - and the Mid-Missouri Mavericks. His college career included Southwestern Illinois College in Belleville, the University of Cincinnati and Coker University in Hartsville, South Carolina. Mueller has coached and sponsored teams in the Mon-Clair League for many years.