This is the 7775th most frequent Polish word.
marsza
"March" (musical or military movement).
The word 'marsza' is used in its accusative form, showing it as the direct object of the verb 'grają'.
Marsza grają na początku uroczystości.
They play the march at the beginning of the ceremony.
Here, 'marsza' is in genitive form, used to indicate 'a moment of' the march.
Po krótkiej chwili marsza, zaczęli tańczyć.
After a brief moment of the march, they started dancing.
In this context, 'marsza' is in accusative form as the direct object of the action 'zagraj'.