Final answer:
The statement is false; a chop block occurs when two offensive players block one defensive player below the knees simultaneously, not merely because a blocker is unseen. A block against an opponent who doesn't see it coming is called a blindside block, which has different legality depending on the league and execution.
Step-by-step explanation:
The statement that a block against an opponent, other than the runner, who does not see the blocker approaching is a chop block is false. A chop block is a specific type of foul in American football that occurs when two offensive players block a single defensive player below the knees at the same time, or if one player hits a defender below the waist while another player is engaging the defender above the waist. A block against an opponent who does not see the blocker coming is often referred to as a blindside block, which can be legal or illegal depending on how it is executed and the rules set forth by the governing body of the league. To ensure player safety, many leagues have implemented rules against certain types of blindside blocks, especially those that involve contact to the head or neck area or are executed with undue force.