My friend had a scratch on his leg before taking the c19 vaccine, four days after vaccine, it got infected, coincidence?

Cuts/scratches on a leg would get infected long before COVID-19/vaccines.  Yes, it is a coincidence.  BTW, the side effect of not getting a COVID vaccine is 553,000 American deaths and counting.  Refusing the vaccine is not being neutral.  BTW, I am a Republican, wear a mask and got vaccinated.

No, it’s not an allergic reaction, and should have nothing to do with a vaccine which would not impact skin staph from causing an infection. It takes several days for a wound to infect as bacteria, staph, have to grow. It would have infected regardless.

Coincidence. It could have gotten infected, if he wasn't taking care of the scratch properly. He should have told the doctor about getting the vaccine. The medications could cause a reaction with it.

Yes. Coincidence. There is no reason the virus or vaccine would have any effect on an open wound.

No.  It's called the immune system got taxed.   Secondary infections are so common they this question is giving me a good laugh. 

Thank you.

i dont think so

Coincidence. Nothing to do with the vaccine.