ABOUT SEKTOR RIVERSIDE
Welcome to Sektor Jiu Jitsu Riverside! Sektor Jiu Jitsu was founded by Sean Roberts in 2016, in Chino, CA. Sean is a highly
respected former world class competitor from the Ralph Gracie lineage. He stopped competing to focus on building the highly competitive Jiu Jitsu team that Sektor is today. In 2019, Sektor Corona opened its doors. Led by Spencer Mendivil, a highly adept teammate of Sean’s, and an immensely skilled teacher; he and his partner Albert run a flourishing program in Corona with many students. In just under a decade, Sektor has opened multiple locations: the original Chino location, Corona, Rowland Heights, Bakersfield (Vindicators), West Covina, and now Riverside.
Sektor Jiu Jitsu now has one of the most formidable kids’ team in the jiu jitsu hotbed of Southern California. Spencer’s student and Sektor Corona competitor, Jeff Chapman, has opened the next Sektor school here in Riverside, CA.
Jeff has been teaching Jiu Jitsu since 2022, and is
focused on creating his own team and community of jiu jitsu athletes. One of the most important aspects of jiu jitsu is the community. We are building a place that is welcoming to all people. Sektor Riverside strives to make jiu jitsu a safe and fun activity for people of every age. With children’s classes starting at age 5, to adults’ classes ranging from ages 13-65+.
Jiu Jitsu teaches people to control opponents with positions and submissions, rather than strikes. While no martial art is without risk of injury, jiu jitsu’s unique style of fighting
allows a student to spar every day without the blows to the head that other martial arts would inflict if they were to spar daily.
So, if you are tired of the mundane workouts at the gym, CrossFit, running, or just sitting on the couch; come, challenge yourself, and get fit by learning jiu jitsu. It’s always challenging and never boring. Come and see what Sektor Jiu Jitsu has to
offer.
Call, text or email to schedule your free class! You’ll be glad you did.
With the goal of getting in better shape, Jeff started jiu jitsu in 2006. Having seen Royce Gracie dominate the UFC, he sought to learn the same ground fighting style at Ralph Gracie Jiu Jitsu in Placentia, CA. There he met Sean Roberts where they were both training under Bruno “Mamute” Paulista. After a long hiatus, in 2015 Jeff started training again under Bruno at Mamute Jiu Jitsu in Anaheim. There, Bruno awarded him his blue belt in Aug 2016.
He moved to Corona in 2017, where he was sidelined by a trail running injury. In Feb 2020, after his daughter Zoey wanted to try jiu jitsu as a way to work out together, they found his new school, Sektor Jiu Jitsu Corona. That is where he met his professor and friend, Spencer Mendivil. He was also reunited with his old teammate Sean Roberts,
whom founded Sektor Jiu Jitsu. Under Spencer, Jeff was awarded his purple belt in 2021, brown belt in 2024, and black belt in 2026.
Jeff also became a very active competitor, and still loves to compete at the highest level.
Some of his accolades are: 2023 JJWL purple belt season champion, JJWL Worlds champion purple belt, IBJJF Pans Masters NoGi bronze medalist brown belt, IBJJF Worlds Masters NoGi silver medalist brown belt, JJWL #1 ranked Masters 3 brown belt heavyweight 2025 season. With many other medals that add to his experience as a competitor.
Although competing is something he enjoys immensely, he found that the best part of jiu jitsu is the community that’s built while training. The joy and fulfillment he got while helping others achieve success, made him want to start teaching and coaching. Jeff started the Sektor Corona fundamentals class in 2022, and has been teaching ever since. Having found a true passion for teaching, he decided to open his own school.
With the mentorship of Spencer, this dream has become a reality.
Jeff Chapman
Owner and Head Instructor
Timmy is a purple belt in Brazilian Jiu-Jitsu with seven years of consistent training and a strong focus on fundamentals. His coaching emphasizes clear instruction, safe training habits, and helping students build confidence through solid technique.
Actively involved in open mat events and the local Jiu-Jitsu community, Timmy values collaboration, shared learning, and creating welcoming spaces for practitioners of all levels. He promotes longevity in the sport by encouraging students to train smart, move with intention, and build sustainable habits that keep them on the mats for years to come.
Timmy Sheldon
Instructor
Sarah is a born and bred Sektor purple belt under Spencer Mendivil. 115 pounds of pure millennial angst, she approaches the mats with a determination to overcome any obstacle and a consistent "just get up" attitude. She will always advocate for accessibility, inclusivity, and for pouring in the milk before the cereal.
Sarah favors structured styles of teaching with a special focus on fundamentals and repetitive drilling. With experience in kids coaching, introductions for beginners, and competition training, Sarah enjoys working with students from any level of experience to help them achieve their own personal goals.
Outside of jiu jitsu, Sarah loves camping, climbing, and long walks down the 99 Ranch snack aisle.
Sarah Razon
Instructor