Coco Gauff’s serve has been one of the most debated technical topics on the WTA Tour this season.

After recording 103 double faults in just 14 matches, many have questioned whether the work with biomechanics expert Gavin MacMillan has actually improved her serve.

But Serena Williams’ former childhood coach Rick Macci offers a very different perspective.

According to Macci, Gauff’s serve is biomechanically better than before. The real issue may not be the structure of the movement anymore.

It may be something else entirely.

Her body.

More specifically: her joint flexibility.

THE HYPERMOBILITY FACTOR

Macci suggested that Gauff’s double-jointed structure creates extra looseness in her arm during the serve.

This means that even when the mechanics are correct, the arm can produce additional micro-movements.

In simple terms:

the system is stable
but the segments are too free.

And that creates variability.

In tennis, variability in the serve is extremely dangerous.

Because the serve is a precision movement executed at very high speed.

Even small uncontrolled movements can alter:

  • racket angle

  • contact point

  • pronation timing

  • ball trajectory

And the result can easily become a double fault.

WHY FLEXIBILITY IS BOTH AN ADVANTAGE AND A RISK

Flexibility is often considered a huge asset in tennis.

Players with high mobility can generate:

  • greater racket head speed

  • more whip effect

  • more spin production

But flexibility without stability can create a different problem.

Control becomes harder.

This is especially true in the serve, where the kinetic chain must transfer energy from the ground to the racket with very precise timing.

If one segment becomes too loose, the chain loses efficiency.

Think of it like a whip with too many soft segments.

The energy disperses instead of traveling cleanly.

THE PLATFORM STANCE IDEA

Macci suggested something interesting: a tighter platform stance.

Why?

Because limiting movement at the base of the chain can stabilize the rest of the motion.

In other words:

reduce degrees of freedom
to increase control.

This is a principle used in many technical sports.

When the body produces too many variables, coaches sometimes simplify the structure to regain consistency.

THE REAL LESSON FOR PLAYERS

The biggest mistake many players make is assuming that every technical issue comes from a flawed technique.

Sometimes the movement is correct.

But the body controlling the movement introduces variability.

In those cases, the solution is not more complexity.

It is often more structure.

Stability before freedom.

Control before power.

Because in tennis, the most effective technique is not the most beautiful one.

It is the one you can reproduce under pressure.