The POST requests carry data that can be processed to add to a database. To differentiate a POST request, the Flask requests object has the method property, which can be checked to see if the request method was GET or POST. If we create a form (called AddForm) to add new arenas to the Arenas table, we could process the data submitted as a POST request and add it the database using the session manager:

from flask import request
from .forms import AddForm
@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.longitude =float(request.form['longitude'])
    arena.latitude = float(request.form['latitude'])
    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)

As this method will accept both GET and POST requests, it sends a different response based on each request method.