Pressing

From the rules (Chapter 11):

Pressing Pressing means that all of your players try to put pressure on their opponents. They also put slightly more effort into breaking up your opponent's attacks than trying to create their own. The result is that the total number of potential chances in the game gets reduced for both teams.
The disadvantage of this tactic is that it will drain the stamina of your players faster than normal.
Two things can greatly increase your chances at successfully reducing the number of attacks in the game: the total defending skill and the total stamina of all your outfield players. If a player has the "Powerful" specialty, his defence skill counts as double for this calculation. Stamina is taken into account for each player when calculating the "pressing skill", so the more tired your players gets, the less able they are to put pressure on their opponents. As always, a player with excellent stamina, or better, has sufficient stamina not to lose any of his skills during the game, at least not out of tiredness. When calculating this "Pressing skill", the experience bonus is added for each outfield player, as normal.
Whenever a potential chance is destroyed by a team using the Pressing tactic, it is reported in the match report. You will never find out which team could have benefited from the chance.
It is perfectly possible for both teams to play Pressing. The effect on reducing the number of potential chances is cumulative and on average, the number of lost opportunities is doubled.

The following statistics gives data for games where one team played pressing against a non-pressing opponent.

		pressing team			opponent			both teams
skill	matches			total			total			total	pressing		possession
1	5	0.00	0.00	0.00	9.00	2.00	11.00	9.00	2.00	11.00	0.20	1.82%	1.5%
2	42	0.05	0.10	0.14	7.76	2.05	9.81	7.81	2.14	9.95	0.33	3.35%	11.5%
3	1061	1.09	0.78	1.87	3.89	2.37	6.26	4.98	3.14	8.12	0.93	11.48%	38.2%
4	9112	1.27	0.95	2.21	2.85	2.77	5.62	4.12	3.71	7.83	1.09	13.86%	43.2%
5	9480	1.11	0.93	2.04	2.53	2.93	5.46	3.65	3.86	7.51	1.09	14.51%	42.8%
6	3818	1.02	0.88	1.90	2.24	3.06	5.30	3.26	3.94	7.20	1.17	16.29%	42.1%
7	1083	1.02	0.87	1.88	2.04	3.09	5.13	3.06	3.96	7.02	1.26	17.93%	42.3%
8	278	1.08	0.77	1.85	1.77	3.15	4.92	2.85	3.92	6.77	1.35	19.86%	41.4%
9	65	0.89	0.69	1.58	1.97	3.58	5.55	2.86	4.28	7.14	1.49	20.91%	39.6%
10	29	0.83	0.66	1.48	1.69	3.45	5.14	2.52	4.10	6.62	1.69	25.52%	42.3%
11	8	1.13	0.88	2.00	2.38	3.13	5.50	3.50	4.00	7.50	1.50	20.00%	46.2%