When Caleb called for someone to go and conquer the giant and take the mountain of Hebron and its territor promised him by Moses and Joshua, he offered his daughter's hand in marriage as a reward. This insured him a valiant son-in-law, he wisely knew! It was Othniel who volunteered. With the giant's overthrow by Othniel, he was given Caleb's daughter. Thus, he acted in faith and gained a position from which he would later be called to confront an even greater enemy of Israel.
We know Caleb and his family was centered in Hebron of Judah, which put him in the extreme south of the Judahite territory, sharing the borderland of Israel with Simeon the southermost tribe. Whether northern ruler or southern ruler, Cushan was a most formidable foe of Israel. Absolutely no other man of Israel could challenge him but God's appointed and anointed man, Othniel, who had already proven himself in response to Caleb's call.