  Vector boson scatterings are fundamental processes to shed light on the
nature of the electroweak symmetry breaking mechanism. Deviations from the
Standard Model predictions on the corresponding observables can be interpreted
in terms of effective field theories, that however undergo consistency
conditions. In this paper, the same-sign W W scattering is considered within
the HEFT context and the correct usage of the effective field theory approach
is discussed. Regions of the parameters space are identified where a signal of
new physics could be measured at HL-LHC with a significance of more than
5$\sigma$ and the effective field theory description is consistently adopted.
These results are then translated into bounds on the $\xi$ parameter in the
composite Higgs scenario. The discussion on the agreement with previous
literature and the comparison with the equivalent analysis in the SMEFT case
are also included.
