This is the 4422nd most frequent Catalan word.
lesionar
To injure or harm.
Here, 'lesionar-se' is reflexive and denotes the action of one harming or injuring oneself.
Ells poden lesionar-se si no fan escalfaments abans de l'entrenament.
They can get injured if they don't warm up before training.
In this sentence, 'lesionar' is used in a causative sense, where one thing or action causes harm or injury to another.
El cop amb la pilota podria lesionar algú al camp.
The hit by the ball could injure someone on the field.
Here, 'lesionar' is describing the direct effect of an event (the fall) causing harm or injury to a specific part (the shoulder).