There are 5 areas worth talking about and I’ll relate each of them back to the Football Fitness terminology and back to the 4 qualities that an ideal performance (X-X-X-X-X) requires.
Football Quickness/Agility is the ability to move freely and quickly in different planes of movement. You might be going in one direction, and suddenly move into a different one without losing speed, strength or balance. This requires a lot of coordination and multi-plane movement training.
In a game, Agility helps you move and react to the flow of the game. Training this also improves your footwork speed.
As I mentioned in the intro, throughout a game, the ideal performance from a(n aspiring) professional footballer is to be able to do these 4 things:
1. Have High Quality Actions (Big X’s)
2. Maintain High Quality Actions (Keeping big X’s throughout the whole game, 90 minutes)
3. Having More Actions (per minute)
4. Maintaining More Actions (per minute)
So the goal is —> X - X - X - X - X - X - X
Agility training will be more directly related to having High Quality Actions. You're sharper, and more able to perform your soccer actions like dribbling at pace, making runs in between players, and tackling an opponent for the ball.
Non-soccer specific drills that isolate this area of fitness include: Ladders, Hurdles, and Cone drills, including a ball when possible makes it more similar to a game and therefore more accepted as a football fitness exercise.
Check out this 9 year old stud go through some amazingly effective Speed, agility, and quickness (SAQ) drills for inspiration in your own training.
I love helping players optimize their soccer careers + lives through actualizing their potential.