Complex sentence: Any other player is available to block, or to be a target for a pass, depending on the play design and modification by the quarterback and center based on what they see the defense doing.
Split into simpler sentences: Any other player is available to potentially block, or to be a target for a pass. Offensive plays have varying levels of protection depending on the play design, and then are modified by the Quarterback and Center based on what they see the defense doing.