Defender Wins Battle Cry Question

“If the defender wins the Battle Cry Test, the charger gains no benefits, plus the defender may immediately use a Reaction to move their model out of engagement with the charger without giving the charger a free attack (see ‘Reactions’, page 41).”

Does the defender only get to move if they have a Reaction marker to spend, or is this a free Reaction?

They can only use one they have available, otherwise it would say “can react” instead of “use a reaction”