At Will Meaning

(idiomatic) at one's preference; as one sees fit

Example:   I'm writing my book at will - there's no deadline or minimum word count.
2013, Ben Smith, "[1]", BBC Sport, 19 October 2013:
  And yet, United always carried the greater threat. Their movement in attack constantly confounded Southampton's defenders, with Rooney, Van Persie and Januzaj swapping places and eluding markers at will.