Player development is about improving the athlete’s skills/technique, their physical qualities such as their strength, power, speed, agility, endurance, and flexibility. The end goal is for the gains in these qualities to carry over to increased sports performance, running faster, jumping higher, hitting harder, cutting quicker/more efficiently, for example.
However, I tend to find that coaches often focus on tactics and neglect to properly address the physical abilities needed to properly implement those tactics. There are huge performance gains left on the table in my opinion by not addressing these components of athlete preparation.
You tend to see coaches perform the sport of choice more so than breaking down components of the sport to enhance performance. It isn’t as simple as doing the sport to become better at it. As a beginner, maybe, but definitely not long term once you have a base level of knowledge of the skills required. Playing the sport itself doesn’t make you faster, stronger, or hit harder, after that entry level of skill gained. This is where proper preparation must come in.
If you want an athlete to perform a specific skill then they have to be able to get into that position physically. This could mean they lack the strength, speed, agility, mobility, or game specific endurance to get there. All the meetings and talking in the world won’t work unless the physical capabilities are there.
As a coach you have two main ways to improve performance. You can improve technique and also physical qualities. The physical qualities have to be specific to the technique, it can’t be random improvements in general physical abilities. This means the muscle contractions must be the same (or very similar), and the strength developed must be through the same range of motion, as a couple of examples.
When planning your sessions, you have to distribute your training time effectively between skills, tactics, and the improvement of physical qualities. Your tactics should work to the strengths of your team’s physical qualities. For example, if you are a rugby league coach you may want to play a power game and try to steam roll teams through the middle of the field. If your players lack size and strength, you have a small forward pack, no matter how much you want to implement that tactic, it is very unlikely your players will be able to implement it due to the lack of physical qualities. This is where you would have to adjust your tactics. You may instead work on speed around the ruck and use their agility (footwork) to gain those quicker play the balls to advance your team up the field.
Have the physical abilities to implement the given skills and then fit your tactics to the capabilities of your team.
For complete player development we have to try our best to bring up all components of performance to optimal levels for a given sport, not maximal levels. For example, a rugby player needs flexibility but they don’t need to be as flexible as a gymnast. How you determine what is optimal will depend on many factors but it is something you can work on over the years to suit the athlete’s style of play, or technique needed for the sport they compete in, and if you coach a team sport you can assess what needs to be trained to implement your tactics optimally.