According to the search results, the answer to the crossword clue "What a marathoner may do around mile 20" is "HIT THE WALL". This phrase refers to the point in a marathon where a runner may experience extreme fatigue and a sudden loss of energy, making it difficult to continue running. Some runners may also experience physical symptoms such as muscle cramps or nausea around this point in the race. To combat hitting the wall, marathoners may use various strategies such as pacing themselves, staying hydrated, and consuming energy gels or other snacks during the race.