Dough is difficult to stretch generally

Affects quality

Usually a flour-strength-to-fermentation-time mismatch.

Ask yourself

How strong is the flour used relative to the style's typical needs?
How long has the dough fermented?

Likely causes

#1
Flour too strong for the fermentation time given
Generally accepted
A high-W or high-protein flour needs proportionally longer fermentation to become extensible; used too soon, it resists stretching.
#2
Dough balls too small for the intended final size
Supported, with regional variation
Underweight dough balls require more aggressive stretching to reach a target diameter, increasing the chance of resistance and tearing.

Rescue it now

Give the dough more resting time before continuing to shape it

Prevent it next time

Match flour strength to your realistic fermentation schedule, and weigh dough balls to the size appropriate for your target diameter

Related

Hand stretching Type 00 flour

Related problems at this stage

Dough is too sticky Dough tears when stretching Dough snaps back when stretching Dough has weak structure (deflates, won't hold shape)