OUR LEADERS
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Michael Mabry
Partner and Co-founder
Michael Mabry is A Partner and Co-Founder of One Play Development, where he leads the organization’s mission to positively impact youth sports. A passionate advocate for holistic athlete development, Michael is committed to empowering athletes to thrive mentally, physically, and emotionally both on and off the field.
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2x Team Captain at Christopher Newport University
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All-State & All-Conference Defenseman
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Champion All-American Game selection (HS)
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Co-Founder of One Play Development (2022)
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Certified EXOS Performance Specialist, Precision Nutrition Coach, and Mental Performance Mastery Coach
As a coach, Michael has held leadership positions in various top high school programs, specializing in player development, team culture, and mental performance. His certifications and experience as a trainer have allowed him to guide athletes through the mental and physical demands of high-level competition. Since co-founding One Play Development, Michael has directly impacted over 4,000 student-athletes, teaching them how to embody confidence, handle challenges, and positively impact others. His leadership in One Play Development continues to influence athletes, club team and high school programs across the country, helping athletes build confidence, overcome challenges, reach their highest potential and directly guide and influence teams toward developing winning records with winning cultures.
Casey O'Neill
Partner
Coach Casey O'Neill combines a storied coaching career with visionary leadership as a Partner at One Play Development, a role he has held since 2021. With 25 years of lacrosse coaching experience—including 14 as Head Coach at Gonzaga College High School—O'Neill's teams achieved:
211-54 career head coaching record | 123-12 WCAC coaching record
9 WCAC Championships | 4× WCAC Coach of the Year
4× Top 3 national finishes (9× Top 25) | 5× Washington Post #1 rankings
15 US Lacrosse All-Americans | 16 All-Met 1st Team selections
2010 All-Met & US Lacrosse (Potomac Chapter) Coach of the Year
His accolades include Washington Post All-Met honors and mentorship of 130+ collegiate players, including 20 who served as college captains. O'Neill's leadership and athlete-first philosophy blend technical mastery with mental performance training.
As Assistant Athletic Director for 14 years, O'Neill oversaw 17 sports and hundreds of coaches, helping elevate programs and student-athletes. A Lehigh University alumnus and recipient of its prestigious "Coach's Award," his NCAA and H.S. lacrosse playing career informs his approach to developing resilient, high-performing athletes and teams.
At One Play Development, O'Neill drives 1v1 development, team building and culture strategy, staff mentorship, while his Mental Performance Mastery Program equips athletes with tools for on-field success and lifelong resilience. His dedication solidifies One Play’s reputation as the nation’s premier lacrosse institution.
Andrew Stimmel
Partner
Andrew Stimmel brings unparalleled leadership and expertise as a Partner at One Play Development, following a distinguished career in NCAA and international lacrosse.
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Captain & Defensive MVP at Ohio State
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Youngest NCAA Head Coach with landmark victories at Marquette
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Team USA Gold Medalist (U-21 Defensive Coordinator)
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Led Yale as offensive coordinator to multiple Ivy League championships and National Championship in 2018
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Developed over 30 collegiate All-Americans and developed 23 PLL, MLL & NLL Draft Picks
A former Captain and Defensive MVP at Ohio State, Stimmel transitioned his on-field success into a prolific coaching career becoming one of the youngest NCAA Head Coaches ever. As the offensive coordinator he achieved national recognition by leading Yale to its first-ever National Championship in 2018, followed by a runner-up finish in 2019. His offenses rank among the most prolific in NCAA history.
Stimmel also served as the Defensive Coordinator at Marquette University, helping the program secure its first-ever Big East Championship in 2016. A proven mentor and innovator, Stimmel’s leadership continues to empower athletes to excel on and off the field. His ability to prepare athletes, their families, as well as club and H.S teams to understand what it takes to go to the next level is a good as can be found. His commitment to winning with integrity drives his approach.
Alec Wortman
Sr. Director
As a Senior Director of Mental Performance at One Play Development, Alec brings over a decade of experience supporting athletes at every level—from youth and high school to NCAA and international competition at the World Lacrosse Championship.
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Former Division I pole vaulter & team captain (University of Maine)
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Master's in Sport & Performance Psychology (National University)
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Key member of One Play Development since 2022
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Specializes in mental strength coaching and athlete mentorship
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Leader in mental performance delivery and program accessibility
Alec combines firsthand athletic experience with advanced education in mindset, neuroscience, and human performance. His work spans individual, team, and organizational levels, creating high-impact programs for athletes, coaches, and teams.
Alec's mental strength coaching focuses not only on tailored mental skills training but also on guiding athletes through the pressures of competition, identity, and personal growth. He leads programs that foster confidence, focus, and resilience, both in-person and online, using science-backed strategies to help athletes unlock their potential.
Mark “Mugs” Mickum
Sr. Director
Mark “Mugs” Mickum is a nationally respected lacrosse goalie specialist with over 30 years of coaching experience in the Washington, D.C. metropolitan area. A former High School All-American at The Landon School and graduate of Washington College, Mickum has dedicated his career to training elite goalies at both the high school and collegiate levels. His coaching accomplishments include:
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30+ years of goalie coaching experience
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10+ High School & College All-Americans developed
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20+ All-State, All-Met, and All-League selections
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3× Markland Kelly Award winners coached
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1 All-Metropolitan Player of the Year
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2 High School National Championships
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30+ Division I goalies mentored | Numerous standout Division III players
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12+ years as Goalie Coach at Georgetown Preparatory School
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Contributor to 15 IAC Championships
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Coaching roles with multiple high school and club programs across the region
Mickum’s goalies have gone on to compete at some of the nation's top academic and athletic institutions, including:
University of Notre Dame, University of Maryland, Syracuse, Harvard, Yale, Penn, Virginia, Johns Hopkins, Navy, Michigan, Villanova, Boston University, Bucknell, Vermont, Colgate, and more.
His decades-long commitment to excellence continues to shape the next generation of top-tier lacrosse goaltenders across the country.
John Rothenberger
Partner and Co-founder
John is a co-founder of One Play Development and the day to day managing business partner. A multi-time successful entrepreneur , John's involvement in the business and One Play's partnership with Volition Partners, a proven startup and early-stage investor, assures viability and long-term success. His commitment to the proper development of athletes, coaches and entrepreneurs brings a unique perspective to the market of youth sports.