Ligaments are bands of tough elastic tissue around your joints. Ligaments in the shoulder connect your humerus to your shoulder blade (also called the scapula). They also connect the clavicle, or collarbone, to the top of your shoulder blade.
When these get stretched, your shoulder becomes unstable. This happens a lot to young people and athletes who put strain on their shoulders, like pitchers in baseball.
You can also sprain or tear your shoulder ligament