Blood in urine once last night after doing sports. Normal in the morning next day. But again in the afternoon. Reason to worry?

Yes. Blood in the urine is never normal. Get evaluated by a urologist.
Could be. Athletics can induce hematuria, but it is unusual. I suggest that you need to see a urologist for cystoscopy and a renal ultrasound. Urinalysis may be helpfule. You need to see your physician.