My cat is limping and in pain after being outside. What should I do?

Hello and thank you for reaching out to Petco Pet Education Center, formerly Petcoach. Based on the information you have provided, and the attached pictures, I am also very concerned that Sprinkles may have sustained significant trauma, causing her to be non-weightbearing lame on her left hind leg. Whether she was hit by a car or potentially fell and injured her leg, it sounds like she is in a significant amount of pain. She also looks like she has abraded skin (a wound) on that leg as well, which is at risk of becoming infected. I recommend having her seen by a veterinarian as soon as possible to have her injuries addressed. He/she will perform a full physical exam to localize her pain and determine if she has other, more life-threatening injuries such as damage to her chest or abdomen. X-rays may be indicated if a fracture is suspected. Ultimately, pain medication and antibiotics can be prescribed to help ease her pain and prevent infection. Importantly, NEVER give pain medication that is intended for humans to your pet, as these can be fatally toxic. I hope this is helpful!