test.java

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final NestedScrollView mParentNestedScrollView = (NestedScrollView) findViewById(R.id.scrollView);
        Button button = (Button) findViewById(R.id.button);
        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

        Observable.interval(50, TimeUnit.MILLISECONDS)
                .subscribeOn(AndroidSchedulers.mainThread())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new rx.Observer<Long>() {
                    @Override
                    public void onCompleted() {

                    }

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onNext(Long aLong) {
                        // scrollXの値によってイベントを起こす..
                        getSupportActionBar().setSubtitle(mParentNestedScrollView.getScrollY() + "px");
                        // Toast.makeText(MainActivity.this, mParentNestedScrollView.getScrollY() + "px", Toast.LENGTH_SHORT).show();
                    }
                });

    }

test.xml

<android.support.v4.widget.NestedScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/scrollView"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        >
        <TextView
            android:overScrollMode="always"
            android:id="@+id/textView0"
            android:layout_width="match_parent"
            android:layout_height="100dp"
            android:background="#ccc"
            />
        <Button
            android:id="@+id/button"
            android:layout_height="wrap_content"
            android:layout_width="wrap_content"
            android:text="push"
            />
    <android.support.v4.widget.NestedScrollView
        android:id="@+id/childScrollView"
        android:overScrollMode="always"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        >
        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            >
        <TextView
            android:overScrollMode="always"
            android:id="@+id/textView1"
            android:layout_width="match_parent"
            android:layout_height="500dp"
            android:background="#333"
            />
        <TextView
            android:layout_below="@id/textView1"
            android:id="@+id/textView2"
            android:layout_width="match_parent"
            android:layout_height="800dp"
            android:background="#999"/>
        </RelativeLayout>
    </android.support.v4.widget.NestedScrollView>
    </LinearLayout>
</android.support.v4.widget.NestedScrollView>

NestedScrollViewはRecyclerViewと相性が悪いらしくて..

http://stackoverflow.com/questions/31000081/how-to-use-recyclerview-inside-nestedscrollview