players that are considered to be leaders in real life are classed as inspirational in the game and that is not trainable but any player in the game can be trained to be a leader, leaders inspire better perfs from players around them, so a CL with a leadership skill of 4 would influence the CR, 5 would be CR and LB 6 would be CR LB & RB 7 would be CR LB RB & SW 8 would also affect the AM and 9 also affects the GK.
inspirational players inspire better perfs from their area irrespective of their leadership skill, so Tony Adams also inspired LB CR and RB to better perfs every week he was on superb morale.
a lot of these bonuses only apply to players on superb morale.