What does it mean when u spit blood sometimes not when i brush my teeth?

Many possibililities: Spitting up blood once awhile, e.g. 1x/yr, might just mean that a tiny blood vessel was torn somewhere along the nasal, oral, food tube, or breathing tube passages, ex: when someone has a cold and blows one' s nose aggressively. However frequent spitting up of blood could indicate a bleeding disorder, a growth, an infection, among other causes along these same areas. See doc if occurs much&often.

Gum Issues: Bleeding upon brushing is not normal. It is a sign of gigivitis or possibly gum disease. You should see a dentist as soon as possible. It is much easier to treat in the early stages.

Periodontitis: Bleeding gums is one of the signs of gum disease and this can be bleeding even when you don't brush your teeth. Seek out a dental professional (dentist or periodontist) for a consultation.