Complex sentence: Bower was the first goaltender to effectively employ the poke check, an aggressive move wherein the goalie uses his stick to poke the puck away from an attacking player, sometimes leaving his crease in the process.
Split into simpler sentences: Bower was the first goaltender to effectively employ the poke check. The poke check is an aggressive move where the goalie uses his stick to poke the puck away from an attacking player, sometimes leaving their crease in the process.