Directory

After being drafted by the National Football League and playing with the Dallas Cowboys and the San Diego Chargers, Sean Lissemore joined the St. Mark’s administrative team as athletic director in 2019. He earned his bachelor’s degree from the College of William and Mary and his master’s degree from Indiana University. A former collegiate football player at the College of William and Mary, he served as team captain and earned All-American honors. He was drafted into the NFL where he played for seven years, including three with the Dallas Cowboys. Sean founded and organized the Sean Lissemore Youth Football Camp, a free enrichment program for children in Dumont, N.J. and was named the San Diego Charger’s NFL Military Salute to Service nominee. Sean is a member of the National Interscholastic Athletic Administrators Association and is a Certified Athletic Administrator. He also serves as eighth grade class adviser.

Mark Sullivan joined the St. Mark's School of Texas faculty in 1982 as the Lower School Physical Education Coordinator. Prior to his appointment as the Director of Athletics and Physical Education in 2000, Mark has served the school as the Wilderness Program Director, the Assistant Head of the Middle School and as a coach and teacher in the Athletic Department. Mark holds a Bachelor of Science Degree and a Masters Degree in Educational Administration from the University of North Texas, and is a recipient of the John H. Murrell Excellence in Teaching Award. Mark's coaching has included numerous Middle School sports as well as the Varsity Volleyball team and the Varsity Diving team.

After a distinguished career in the military, which included stints as a cannon crewman, a military intelligence officer and several tours in Iraq and Afghanistan, Reyno Arredondo ’87 returned to his alma mater in 2017 as head wrestling coach. He earned his Bachelor of Science degree from the United States Military Academy at West Point and a Master of Arts degree from the University of Texas at Austin. During his military career he taught in the Department of Foreign Languages and Behavioral Sciences and Leadership, as well as serving as an associate athletic director in the Directorate of College Athletics, Army-West Point. At St. Mark’s he is also a physical education teacher for Middle and Upper School students, seventh grade baseball coach, seventh grade adviser and sponsors the Martial Arts Club. He’s an inductee in the Texas Wrestling Hall of Honor and was awarded three Bronze Stars and earned Airborne and Air Assault wings during his military service.

Natalie Bumpas has been a member of the School’s athletics staff since 2020 and currently serves as athletic trainer. She earned a bachelor’s degree from Indiana University and a Master of Arts degree from the University of Iowa. Before coming here, Bumpas served as an associate athletic trainer at Northwestern University and as an assistant athletic trainer at the University of Nebraska-Omaha. She also interned for the New York Mets during the 2011 season. Bumpas is nationally certified by the National Athletic Trainers’ Association (NATA) Board of Certification, and has been a member of NATA since 2004. She is also a licensed athletic trainer in the state of Texas and recently became certified in Graston Technique for soft tissue mobilization.

After playing football at Princeton University, Harry Flaherty spent brief stints with the New Orleans Saints, Tampa Bay Buccaneers and Dallas Cowboys before moving to the University of Tennessee, where he earned a law degree while coaching football in a graduate assistant role for the Volunteers’ football program. Coming to St. Mark’s in 2021, he now serves as head football coach, Upper School history teacher and adviser in the 11th and 12th grade rotations. Before joining St. Mark’s, Flaherty spent six years at The Lawrenceville School in New Jersey, where he served as a history teacher, head varsity football coach, assistant dean of Admission and housemaster for all ninth grade boarding boys.

Cameron Hillier ’13 returned to his alma mater in 2020 as a member of the English Department, where he teaches classes in junior English, literature of war and survival and dystopian literature. Before returning to St. Mark’s, he earned a bachelor’s degree from Colby College. Hillier is the head tennis coach here, directs the School’s Wilderness Program and serves as an adviser in the freshman-sophomore class rotation. He also taught English at Christ School in Asheville, NC while coaching tennis and serving as head of house for one of the campus dormitories there.

Matt Hjertstedt has been a member of the St. Mark’s community since 2008 and serves as head athletic trainer in the Athletic Department, where he also teaches Middle School physical education and health classes. He earned his Bachelor of Science degree from Central Washington University and Master of Science degree from Texas Tech University Health Sciences Center. He’s also a certified athletic trainer and a licensed athletic trainer. Before joining St. Mark’s, Hjertstedt worked in the fitness industry as a personal trainer and strength coach. A dad to current Marksman Westin ‘31, he also spent time working at Harborview Medical Center in Seattle in the Acute Rehab Unit. Hjertstedt also sponsors an independent studies course in sports medicine for Upper School students and received the John H. Murrell Excellence in Teaching Award in 2014.

After a collegiate coaching career at Mary Hardin-Baylor University, Darren Teicher joined the St. Mark’s faculty in 2008 where he serves as head volleyball coach. He earned a bachelor of science degree from the University of Mary Hardin-Baylor, where he won a national championship as a player. As a coach here, his teams have won seven SPC volleyball championships.

Trey Whitty joined the St. Mark’s faculty in 2022 and is the head lacrosse coach. Whitty earned a Bachelor of Arts degree from the University of Virginia. Prior to joining St. Mark’s, Whitty served as the head lacrosse coach and director of athletics at St. Paul’s School in Brooklandville, MD. He has also taught and coached at McDonogh School and St. Mary’s High School in Maryland. Whitty teaches Middle and Upper School physical education, is a 12th grade adviser and the head coach of the eighth grade football team. Whitty is a two-time USA Lacrosse Assistant Coach of the Year recipient.