  The physical properties of itinerant antiferromagnetic (AFM) SrCr$_2$As$_2$
with body-centered tetragonal ThCr$_2$Si$_2$ structure were investigated in
single crystalline and polycrystalline forms by electrical resistivity $\rho$,
heat capacity $C_{\rm p}$, magnetic susceptibility $\chi$ versus
temperature~$T$ and magnetization $M$ versus applied magnetic field $H$
isotherm measurements as well as $^{75}$As and $^{53}$Cr nuclear magnetic
resonance (NMR) measurements in the wide temperature range $T$ = 1.6--900 K.
From the $\chi(T)$ and $^{75}$As NMR measurements, the G-type AFM state below
$T_{\rm N}$ = 615(15) K has been determined, consistent with the previous
neutron-diffraction measurements. Direct evidence of magnetic ordering of the
Cr spins was shown by the observation of the $^{53}$Cr NMR spectrum under $H$ =
0. From the $\chi(T)$ measurements on single-crystal SrCr$_2$As$_2$ under the
two different magnetic field directions $H||ab$ and $H||c$ in the AFM state,
the Cr ordered moments are shown to align along the $c$ axis in the G-type AFM
state. The metallic state is directly evidenced by the $\rho$, $C_{\rm p}$, and
NMR measurements, and the density of states at the Fermi energy ${\cal
D}(E_{\rm F})$ in the AFM state is estimated to be 7.53 states/eV f.u. for both
spin directions which is almost twice the bare ${\cal D}(E_{\rm F})$ estimated
from first-principles calculations, suggesting an enhancement of the
conduction-carrier mass by a factor of two in the AFM state. The ${\cal
D}(E_{\rm F})$ is found to be nearly constant below at least 100 K and is
independent of $H$. The $\rho(T)$ is found to show $T$-linear behavior above
$T_{\rm N}$ and exhibits positive curvature below $T_{\rm N}$ where significant
loss of spin-disorder scattering upon magnetic ordering is observed.
