U21 matches have several differences compared to normal matches.
The Most obvious difference is that U21-matches are played with 7 vs 7. You are allowed to use all 6 substitutes (instead of just 3) so you can let a total of 13 players get experience per youth match.
There are some line-up positions specific to 7 vs 7 matches (LCB, RCB etc). These positions cover both the center and one of the flanks.
U21 matches have no attendance and they do not affect your popularity (number of fans). You also can't sell tickets for those matches.
When you, as manager, watch one of your U21 matches live you get 0.5 credit. This is the same for both home and away matches.
Players are less likely to get injured in U21 matches and they are also less likely to get cards. Cards in U21 friendlies are also valid for real friendly matches and cards for U21 league matches can also lead to suspension from official league matches.
The field still consists of the same number of sections. Players are a little faster in U21 matches to reflect that the field is actually smaller than an 11x11 field.
U21 matches count as matches in the official category. They give your players 90% of the experience they would get in official matches.
You can't analyse youth matches, even if you have a scout's office. This feature is only available for normal matches.
