Groin guard
From wipipedia.org

Jockstrap containing groin guard
A groin guard is a hard cover placed over the male genitals to protect them, especially when playing sports such as cricket or boxing. It is also known as a groin box, groin cup or groin protector. It is also sometimes called a groin pad, but strictly speaking that is something different.
The guard should be worn in a garment, such as a jockstrap, specifically designed to accommodate it. It should fit tightly against the body or it may shift when hit, hurting the genitals.