The 100 Thieves Rocket Mortgage house, three stories of light-colored wood and concrete, sits on a quiet block of Venice, Calif. It’s the “League of Legends” practice house for 100 Thieves, an 18-month-old esports team and lifestyle brand sponsored by Rocket Mortgage, whose logo is splashed across the walls. Inside, professional gamers practice the fantasy battle arena game in preparation for tournaments around the world. On a recent morning, marketing and operations staff buzzed around the expansive second floor while footage from the previous day’s “League of Legends” world championships played on a large screen. Matthew...