駆けっこ
かけっこ · kakekko · JLPT N1 · noun
race
🏁 駆ける (to run) + っこ casual noun suffix = a running contest, the verb stem made into a noun
駆ける means to run or gallop, and its kanji 駆 carries the 馬 (horse) radical on the left. Adding the casual suffix っこ turns the verb stem into a noun for a race on foot.