1,926. Men Who Can Only Perform Chalitzah (But Not Yibum)
Yibum v’Chalitzah 6:4
The following brothers are able to perform chalitzah but not yibum: those in doubtful situations, such as whether a yevama is prohibited to the yavam; a man with crushed testicles, a severed male member, or some other form of castration; an elderly man who is no longer virile enough to perform yibum. If a castrated man is intimate with his yevama, he does acquire her as a wife because there was a point in time when he was able to father children. He must nevertheless give her get because he is prohibited to enter the general marriage pool. A person of indeterminate gender performs chalitzah to the exclusion of yibum because his gender is in doubt. If an operation reveals that he is male, he may then perform either chalitzah or yibum. Other brothers may perform either chalitzah or yibum, as they may prefer.
Yibum v’Chalitzah 6:5
Some yevamos can perform either chalitzah or yibum; some may not perform either yibum or chalitzah. The latter have no levirate bond at all and are permitted to marry other men. Some yevamos can perform chalitzah but not yibum, and some can perform yibum but not chalitzah.