Should have been offside.
The whole "deliberate play on the ball" is supposed to be in reference to a player actually trying to possess or control the ball in a specific direction (to one's self, teammate, etc.).
The "deliberate play" is not a defending slide or tackle.
In the circumstance that
@coolguy was mentioning about a headed attempt, this same example was used by a referee assignor/coordinator/educator to a group of coaches I was with. A headed ball
should be a controllable ball, especially one that allows for a defender to be stationary and jump for a challenge. An attacking team is not supposed to be punished because a defending team is poor at controlling a ball. An attacker can still gain an unfair advantage by being in an offside position with the "new" offside application.