Solution: Behaves like a fool, informally - NYT Crossword

This is a debut and a really fun term, one of those with confusingly opposite definitions. I first learned this one — someone who blows the lead or makes a big blunder ACTS THE GOAT — and figured it was a natural shortening of “scapegoat.” (This is probably true, although there’s at least one tantalizing reference to a story about a goat pulling a peanut cart.) 58D: “Surrender” doesn’t fit, so this is one down entry that had to wait for crosses galore. Apparently, a white flag can indicate that the leader of a race is in the FINAL LAP, or it can indicate a slow-moving vehicle ahead; a white flag with a red cross can mean the last lap has been reached, but it can also mean there’s an ambulance on the course.