  The ALICE collaboration recently reported the mean transverse momentum as a
function of charged-particle multiplicity for different pp-collisions classes
defined based on the "jettiness" of the event. The event "jettiness" is
quantified using transverse spherocity that is measured at midpseudorapidity
($|\eta|<0.8$) considering charged particles with transverse momentum within
$0.15<p_{\rm T}<10$ GeV/$c$. Comparisons to PYTHIA 8 (tune Monash) predictions
show a notable disagreement between the event generator and data for jetty
events that increases as a function of charged-particle multiplicity. This
paper reports on the origin of such a disagreement using PYTHIA 8 event
generator. Since at intermediate and high $p_{\rm T}$ ($2<p_{\rm T}<10$
GeV/$c$), the spectral shape is expected to be modified by color reconnection
or jets, their effects on the average $p_{\rm T}$ are studied. The results
indicate that the origin of the discrepancy is the overpredicted multijet yield
by PYTHIA 8 which increases with the charged particle multiplicity. This
finding is important to understand the way transverse spherocity and
multiplicity bias the pp collisions, and how well models like PYTHIA 8
reproduce those biases. The studies are pertinent since transverse spherocity
is currently used as an event classifier by experiments at the LHC.
