Help Reading a Injury

Playing 70's League.
Mota sustains a gb injury vs. LHP with runners on 1st and 3rd - no out. Runner on 1st advanced to 2nd and runner on 3rr held - Mota out.
4/5 of Mota's injuries vs LHP are:
$3-gb A + injury
3-gb A + injury
3-gb A + injury
3-gb A + injury
Trying to get a read and also Puzzled as to why the result was not a DP?

With a man on 3rd and none out the infield was probably in, which over-rules the gb(A).