BACKGROUND: Low back pain (LBP) is a common condition that can affect athletes of all ages. The risk factors for LBP onset and worsening associated with the lacrosse shooting motion are not yet known. PURPOSE: To identify training and biomechanical factors associated with preexisting LBP and development of LBP over 6 months in youth, high school, and collegiate lacrosse players. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: A total of 128 lacrosse players were enrolled in this study between January 2016 and January 2019. Player characteristics, lacrosse experience, and participation in other sports were self-reported. At baseline and 2-, 4-, and 6-month follow-ups, the players self-rated the presence and severity of LBP using a numeric pain rating scale (0-10 points). Participants were grouped according to LBP symptoms: no LBP at any time point (n = 102), preexisting LBP (n = 17), or developed LBP within the 6-month period (n = 9). The lacrosse shooting motion was captured via 3-dimensional motion analysis, and kinematic and kinetic variables were recorded. A Low Back Stress Index was used to estimate lumbar stress as a function of pelvic acceleration at the time of maximum lateral trunk lean during the shot. Univariate analyses of covariance and logistic regression models were used to address study aims. RESULTS: Compared with the no-LBP group, the preexisting LBP group demonstrated 13.9% to 22.9% lower maximum angular velocities at the pelvis, trunk, and shoulders in the transverse plane ( < .05), 19.3% less collective pelvis-shoulder rotation in the transverse plane ( = .015), and 4.5% more knee flexion excursion ( = .063). The developed-LBP group produced 2.3% to 11.1% higher angular velocities in the pelvis, trunk, and shoulder and generated maximum pelvic acceleration values 36% to 42% higher than the remaining groups ( < .05 for both). Mean Low Back Stress Index values were not statistically significant among the groups (no LBP: 12,504 ± 13,076 deg/s; preexisting LBP: 8808 ± 10,174 deg/s; developed LBP: 19,389 ± 13,590 deg/s; = .157). CONCLUSION: Preexisting LBP was associated with significantly restricted motion of the pelvis, trunk, and shoulders during a lacrosse shot. Excessive pelvic acceleration may be related to the development of LBP in lacrosse players.