[5][6] He concentrated on athletics after an incident in fifth grade in which classmates teased him for remaining in costume and makeup after a drama competition.

[6] Starting with his sophomore year in high school, Mertens was active in Young Life, a national organization that preaches Christianity to youth.

The school's football team competes in National Collegiate Athletic Association (NCAA) Division III.

[11][12] In January 2014, Mertens came out as bisexual, the first active college football player at any level to publicly come out.

[6][12] With his announcement, he was banned from working with Young Life, which he had been certain would be a part of the rest of his life; the organization's "Faith and Conduct Policies" did not allow any LGBT person to be a staff member or volunteer, though they could participate as "recipients of ministry of God's grace and mercy as expressed in Jesus Christ.