This is the 10062nd most frequent Catalan word.
omplen
"Omplen" means "they fill" in English.
'Omplen' is used here as the conjugated form of the verb 'omplir' in the third person plural, indicating the act of filling or occupying a space.
Les flors omplen el jardí de colors.
The flowers fill the garden with colors.
'Omplen' is used reflexively as 's'omplen' to indicate that the subject (ditches) is being filled by external conditions without specifying an agent.
Quan plou, les fosses s'omplen ràpidament.
When it rains, the ditches fill up quickly.
Here, 'omplen' demonstrates the action performed by the subject (fans) filling the area (arena) purposefully.