Your throwing shoulder loses internal rotation compared with the other side. The working convention is: keep the side-to-side difference under roughly 20 degrees.
GIRD is the abbreviation that turns up in every shoulder guide and never gets spelled out: the internal rotation deficit of the throwing shoulder. It sits in more external rotation than the other side but loses internal range — the price of thousands of throws. The classic mistake is staring at one absolute figure. What counts is the side-to-side comparison: how much worse does the throwing shoulder rotate inwards than the other one? Check it regularly, and have a coach or physio run the GIRD check once if you want the exact number. The remedies are the posterior capsule via the sleeper stretch and strength for the external rotators. One honest note: the widely quoted 20-degree mark is a practical convention with a biomechanical rationale, not a threshold fixed by meta-analysis — what matters is not a single number but a gap that grows across the season.