oh ok thanks but still his leg got cracked up
I hate having to explain this time and time again to loads of people.
Nami wore down Sanjis body. Muscles serve two primary functions, to allow movement and to act as shock absorbers when the body takes an impact. When a muscle is worked hard or fatigued the muscle fibers pull themselves apart and rebridge the gap. This is called muscular hypertrophy, making the latter role impossible to be fulfilled, bones are brittle. Bones breaking because of this are called stress fractures.
Sanjis fracture was NOT due to Weaker Haki or being weaker in general.
Sanji can't really show it on panel because of his black trousers, so unless he fights with bare legs we can't tell until he hits a Logia user. However Luffy has stated that Sanji can use Busoshoku Haki. He demonstrated Kenbushoku Haki in the toxic lake looking for Kin'emons torso.
