The adjective disabling describes something that's devastating in some way, usually physically. When an accident is disabling, it's a terrible one, resulting in someone being badly injured.
A disabling car crash isn't one in which the passengers walk away unharmed, and if a person is diagnosed with a disabling disease, she can expect it to dramatically affect her life. People affected by a disabling event are often left incapacitated — unable to walk, for example. Disabling comes from disable, with its roots of dis, or "do the opposite of," and ablen, "to make fit."