using groovy playground

sample.groovy

import groovy.json.JsonSlurper

def jsonSlurper = new JsonSlurper()
def object = jsonSlurper.parseText(
          '{"count":20,"teams":[{"id":322,"name":"Hull City FC","shortName":"Hull","squadMarketValue":null,"crestUrl":"http://upload.wikimedia.org/wikipedia/de/a/a9/Hull_City_AFC.svg"},{"id":338,"name":"Leicester City FC","shortName":"Foxes","squadMarketValue":null,"crestUrl":"http://upload.wikimedia.org/wikipedia/en/6/63/Leicester02.png"},{"id":340,"name":"Southampton FC","shortName":"Southampton","squadMarketValue":null,"crestUrl":"http://upload.wikimedia.org/wikipedia/de/c/c9/FC_Southampton.svg"}]}'
)

def allTeamNames = object.teams.name
def namesWithCity = object.teams.findAll {it.name =~ /City/}.name