{
    "_id" : ObjectId("58760d8caa30c585ef8d3beb"),
    "results" : [
        {
            "item" : "A",
            "score" : 5.0,
            "answers" : [
                {
                    "q" : 1.0,
                    "a" : 4.0
                },
                {
                    "q" : 1.0,
                    "a" : 5.0
                },
                {
                    "q" : 2.0,
                    "a" : 6.0
                }
            ]
        },
        {
            "item" : "B",
            "score" : 8.0,
            "answers" : [
                {
                    "q" : 1.0,
                    "a" : 7.0
                },
                {
                    "q" : 1.0,
                    "a" : 5.0
                },
                {
                    "q" : 2.0,
                    "a" : 9.0
                }
            ]
        }
    ]
}

{
    "_id" : ObjectId("58760d8caa30c585ef8d3beb"),
    "results" : [
        {
            "item" : "A",
            "score" : 5.0,
            "answers" : [
                {
                    "q" : 2.0,
                    "a" : 6.0
                }
            ]
        },
        {
            "item" : "B",
            "score" : 8.0,
            "answers" : [
                {
                    "q" : 2.0,
                    "a" : 9.0
                }
            ]
        }
    ]
}

db.getCollection('test').update({"results.answers.q":1},
                                { $pull: {"results.$.answers": {q:1} } },
                                { multi: true })

{
    "_id" : ObjectId("58760d8caa30c585ef8d3beb"),
    "results" : [
        {
            "item" : "A",
            "score" : 5.0,
            "answers" : [
                {
                    "q" : 2.0,
                    "a" : 6.0
                }
            ]
        },
        {
            "item" : "B",
            "score" : 8.0,
            "answers" : [
                {
                    "q" : 1.0,
                    "a" : 7.0
                },
                {
                    "q" : 1.0,
                    "a" : 5.0
                },
                {
                    "q" : 2.0,
                    "a" : 9.0
                }
            ]
        }
    ]
}

db.getCollection('test').update({},{ $pull: {"results":{"answers": {$elemMatch:{q:1} }} }},{ multi: true });