Ability to generate force quickly is a primary evaluation protocol for assessing athletic potential. Jumping indices have become major indicators of potential or judging training improvement. However, there is limited information concerning these indices for college football players. PURPOSE: To compare two forms of reactive strength index (RSI) between college football linemen and backs. METHODS: Linemen (n = 11) and backs (n = 12) from an NCAA D-II program were tested for one-repetition maximum (1RM) squat (SQ), paused squat jump (SJ) and drop-jump vertical jump (DVJ) determined from reach height. Flight time during SJ and ground contact time (GCT) were measured using an automated contact mat. Each player performed 3 trials of each jump. Relative 1RM SQ was expressed allometrically (SQ/kg0.67). RSI was calculated as a ratio of DVJ to GCT (RSI-1) and Ft/GCT (RSI-2). Data were analyzed with ANOVA and significance was accepted with p<0.05. RESULTS: Linemen were significantly taller (186.7 ± 3.6 cm) and heavier (117.3 ± 15.7 kg) than backs (180.1 ± 6.0 cm and 90.1 ± 5.3 kg, respectively). 1RM SQ was greater in linemen (200.0 ± 26.7 kg) than backs (182.7 ± 28.4 kg), but relative SQ was similar (linemen: 8.20 ± 1.05; backs: 8.99 ± 1.32). Reliability for GCT (ICC = 0.922), Ft (ICC = 0.990), DVJ (ICC = 0.960), and SJ (ICC = 0.991) was high. RSI-1 (2.12 ± 0.52) was greater than RSI-2 (2.04 ± 0.54), although they were highly correlated (r = 0.93). RSI-1 and RSI-2 were greater in backs (2.33 ± 0.38 and 2.42 ± 0.46, respectively) than in linemen (1.67 ± 0.49 and 1.91 ± 0.48, respectively) with large effect sizes (ES = 1.52 and 1.07, respectively). Relative SQ was moderately correlated with RSI-1 (r = 0.63) and RSI-2 (r = 0.59), but there was no relationship with 1RM SQ (r = 0.06 and 0.13, respectively). RSI-1 and 1RM SQ correctly classified 80% of linemen and 85% of backs to the proper position. CONCLUSION: Ratios utilizing contact time appear more effective at evaluating reactive strength than measurements of strength or simple jump performance (jump height). The relationship between relative strength and reactive jumps suggests that players who have greater relative strength can move more effectively in reactive situations which may more accurately identify performance potential in college football players.