  In this letter, we report the discovery of an intriguing HVS (J1443+1453)
candidate that is probably from the Sagittarius Dwarf Spheroidal galaxy (Sgr
dSph). The star is an old and very metal-poor low-mass main-sequence turn-off
star (age $\sim14.0$ Gyr and [Fe/H] $= -2.23$ dex) and has a total velocity of
$559.01^{+135.07}_{-87.40}$ km s$^{-1}$ in the Galactic rest-frame and a
heliocentric distance of $2.90^{+0.72}_{-0.48}$ kpc. The velocity of J1443+1453
is larger than the escape speed at its position, suggesting it a promising HVS
candidate. By reconstructing its trajectory in the Galactic potential, we find
that the orbit of J1443+1453 intersects closely with that of the Sgr dSph
$37.8^{+4.6}_{-6.0}$ Myr ago, when the latter has its latest pericentric
passage through the Milky Way. The encounter occurs at a distance
$2.42^{+1.80}_{-0.77}$ kpc from the centre of Sgr dSph, smaller than the size
of the Sgr dSph. Chemical properties of this star are also consistent with
those of one Sgr dSph associated globular cluster or of the Sgr stream member
stars. Our finding suggests that J1443+1453 is an HVS either tidally stripped
from the Sgr dSph or ejected from the Sgr dSph by the gravitational slingshot
effect, requiring a (central) massive/intermediate-mass black hole or a
(central) massive primordial black hole in the Sgr dSph.
