First come typically. Thurs and sats DPR has the courts reserved. 6-8p on thurs and 8a-12p on sats. Hope this helps.
Melissa is absolutely correct. As the season moves toward the winter, the courts generally get busy until nightfall. I understand that you can still reserve a court on the DC DPR website; https://dpr.dc.gov/page/athletic-fields-courts#
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