Here's a breakdown of his defensive stats, over 3182 PAs and 6480 innings, almost all in RF.
Career DEF (includes position+UZR): -21.9 (-4.1 DEF/600 PA)
Career UZR: 14.6 (2.8 UZR/150)
Career DRS: -12 (-2.3 DRS/600)
Career dWAR: -4.8 (-0.9 dWAR/600)
That's not so bad - it's a below-average defender at a position on the bottom of the spectrum, but not one who is incapable of playing the field.
However, if we look at Cruz's stats from just the last three years, we get a far different story.
Last 3 years DEF: -33.1 (-12.3 DEF/600)
Last 3 years UZR: -14.2 (-4.6 UZR/150)
Last 3 years DRS: -21 (-7.8 DRS/600)
Last 3 years dWAR: -4 (-1.5 dWAR/600)
That's significantly worse across the board (and in a reasonable sample, 3 seasons of data).
Markakis is worse over both his career and the last three seasons by UZR/DEF but better by DRS/dWAR. And of course there's the longstanding argument over Markakis and whether the stats match the eye test, while with Cruz, the eye-test consensus seems to be that he's a serious negative in the field.
RZNJ specifically asked for a comparison to Markakis' bb-ref numbers, so here they are, for reference:
Career DRS: 5 (0.6 DRS/600)
Career dWAR: -4.2 (-0.5 dWAR/600)
Last 3 years DRS: -12 (-3.8 DRS/600)
Last 3 years dWAR: -2.9 (-0.9 dWAR/600)
Cruz has been about half-a-win per season worse, both over their respective careers and over the last 3 seasons.
Also for reference, here are Nate McLouth's numbers over his 1.5 seasons with the Orioles:
DEF: -5.3 (-3.8 DEF/600)
UZR: 3.3 (4.5 UZR/150)
DRS: -1 (-0.7 DRS/600)
dWAR: -0.8 (-0.6 dWAR/600)
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