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The box() method for returning futures does cause an additional allocation to the heap. Another method of returning futures relies on using a nightly version of Rust or for this issue  https://github.com/rust-lang/rust/issues/34511 to be resolved. The new async_add_points() method would return an implied Future trait and would look as follows:

fn async_add_points<F>(f: F, player: &mut Player, points: u32) -> impl Future<Item = Player, Error = F::Error>
where F: Future<Item = Player>,
{
    // Presuming that player.add_points() will send the points to a  
    // database/server over a network and returns
    // an updated player score from the server/database.
    let _ = player.add_points(points).flatten();

    // Additionally, we may want to add logging mechanisms, friend 
    notifications, etc. here.

    return f.map(player.clone());
}