scratch
The Spanish phrase 'hacer(se) un arañazo' translates to 'to get a scratch' in English. It can be used to refer to accidentally injuring oneself by scratching or being scratched, typically against a sharp or rough surface. In Spanish it is a reflexive verb, hence sometimes used as 'hacerse un arañazo', where 'se' refers to oneself.
Juan scratched himself playing football.
This sentence means that while Juan was playing football, something happened that caused him to scratch himself. The verb 'hacerse' is being used in the reflexive form, implying that the subject did the action to himself.
Because I didn't wear gloves, I scratched myself cutting the roses.
The speaker in this sentence indicates that they got a scratch from cutting roses due to not wearing gloves. The verb 'hacerse' here is used reflexively to indicate that the speaker unintentionally caused the scratch to himself.
If he keeps climbing that tree, he's going to scratch himself.
This sentence is a warning or prediction. The speaker predicts that the person climbing the tree will end up scratching themselves if they continue. The verb 'hacerse' is used here to show that the subject may unintentionally cause the action to himself.