In his fight with Valt, Free was injured, and that's why he had to Forfeit his match. But, how did Free get that injury?
While he was fighting with Valt, he was pushing himself by trying to accumulate enough strength to battle at his fullest power. But he ended up using too much energy, which led to his injury. He was in so much pain, he had to forfeit his match.
Source: Beyblade Wiki
yes he did, while he was fighting Vault with his bey he overexerted himself and ended up pulling a muscle I believe in his shoulder, which led to him having to Forfeit the match as well as not being able to Beyblade until his shoulder got better, this is a similar situation to what shu did in Beyblade burst and Beyblade burst evolution at the end when he went up against volt when they did that 18 round battles. free had already been exerting too much energy during his special training when he was pulling the rocks and forcing himself to go over and above his limit. but by him doing so it cost him a lot of pain and that's how he basically got the injury.