Unmark a match as underway

{
    "match": {
        "attachment_count": null,
        "created_at": "2015-01-19T16:57:17-05:00",
        "group_id": null,
        "has_attachment": false,
        "id": 23575258,
        "identifier": "A",
        "location": null,
        "loser_id": null,
        "player1_id": 16543993,
        "player1_is_prereq_match_loser": false,
        "player1_prereq_match_id": null,
        "player1_votes": null,
        "player2_id": 16543997,
        "player2_is_prereq_match_loser": false,
        "player2_prereq_match_id": null,
        "player2_votes": null,
        "round": 1,
        "scheduled_time": null,
        "started_at": "2015-01-19T16:57:17-05:00",
        "state": "open",
        "tournament_id": 1086875,
        "underway_at": null,
        "updated_at": "2015-01-19T16:57:17-05:00",
        "winner_id": null,
        "prerequisite_match_ids_csv": "",
        "scores_csv": ""
    }