Rugby union is a field invasion sport that requires a variety of high-level physical qualities, in particular, ballistic qualities such as sprinting and jumping. A key physiological mechanism that contributes to ballistic performance in the stretch shortening cycle (SSC), as well as muscular strength. The isometric contraction of the plantar flexors provides tension for the series elastic component to absorb and reproduce energy effectively and contribute to SSC performance. Therefore, the aim of this dissertation was to review current literature exploring the relationship between isometric plantar flexor strength and ballistic performance as well as the underlying mechanisms, followed by an investigation into the relationship in plantar flexor isometric strength and ballistic performance in provincial level rugby union players. Twenty-nine men provincial rugby players (age: 19.3 – 34.1; weight: 82.3 – 124.4 kg) participated in this investigation. Maximal seated and standing isometric plantar flexor strength, countermovement jump (CMJ), pogo jump and 30m sprint were performed. Isometric seated and standing planter flexor metrics (peak force, impulse at 100ms, 150ms and 200ms, and peak vertical force) were analysed using a correlation analysis, along with CMJ (jump height, peak power, flight time/contraction time ratio and concentric peak force), pogo jump (contact time and reactive strength index) and sprint (F0, V0, Pmax, max speed, 10m, 20m and 30m splits) metrics. Standing isometric plantar flexor peak vertical force on the left and right leg were significantly correlated to CMJ jump height (p < 0.03; r = 0.570-0.551), standing isometric plantar flexor peak vertical force on the left leg was significantly correlated with CMJ peak power (p < 0.05; r=0.501), and seated isometric plantar flexor peak vertical force on the left leg had a significant correlation with flight time and contraction time ratio (p ≤ 0.05, r=0.514). The findings of this investigation indicate that maximal isometric plantar flexor strength may provide insight into the overt execution of slow SSC actions, but not for fast SSC movements.