The view function that will process the request accepts both GET and POST request methods. The endpoint '/add' is used in this case, though it could have been anything that differentiated it from the arena endpoint:

@app.route('/nba/api/v0.1/arena/add', methods=['GET', 'POST'])
def add_arenas():
  form = AddForm(request.form)
  form.name.data = "New Arena"
  form.longitude.data = -121.5
  form.latitude.data = 37.8
  if request.method == "POST":
    arena = Arena()
    arena.name = request.form['name']
    arena.latitude = float(request.form['latitude'])    
    arena.longitude = float(request.form['longitude'])
    arena.geom = 'SRID=4326;POINT({0} {1})'.format(arena.longitude, arena.latitude)
    session.add(arena)
    data = [{"type": "Feature", "properties":{"name":arena.name}, 
    "geometry":{"type":"Point", 
    "coordinates":[round(arena.longitude,6), round(arena.latitude,6)]},}]
    return jsonify({'added':'success',"type": "FeatureCollection","features":data})
  return render_template('addarena.html', form=form)

Once the button is pushed, the data is submitted. The view function will determine what to do based on the request method—if it is a POST request, the data submitted in the form will be used to create a new arena object, and the session manager will save the object, adding it to the database.