Injury to the Ulnar Collateral Ligament (UCL) is common among baseball pitchers, due to high external valgus torques applied around the elbow during pitching. Literature shows that elbow muscles and the osseous articulation can lower the load imposed to the UCL by countering the external valgus moment. As the contribution of the individual elbow muscles and the osseous articulation to the UCL load during pitching remains unclear, this study aims to identify the muscles capable of (un)loading the UCL during baseball pitching. Muscle-driven simulations for ten baseball pitches were generated using a musculoskeletal (MSK) model of the upper extremity. The simulations were run twice: ones without any constrictions to the model and ones with the wrist motion locked. The flexor digitorum superficialis (FDS) was identified as biggest contributors to the internal muscle moment during the wrist-included simulations. The external valgus torque was 10% countered by the elbow muscles, 59% by the osseous articulation and 31% by the UCL. The UCL had to resist a moment of 25.6 Nm. During the wrist-excluded simulations, the flexor carpi radialis (FCR) and was identified as biggest contributors to the internal muscle moment. The external valgus torque was 10% countered by the elbow muscles, 42% by the osseous articulation and 48% by the UCL, resulting in a UCL moment of 39.4 Nm. Further research should focus on the influence of wrist and finger motion on UCL load and concentrate more on the osseous articulation as main elbow stabilizer during pitching.