Team opponent batting average is another way of saying batting average against (as allowed by a team's pitching staff).
More about Team Opponent Batting Average
With the decline in offense overall batting average has gone down in recent years, as nearly half of pitching staffs allowed a batting average below .250 in 2013. The decline in batting average is largely due to the increase in strikeouts (thus fewer balls put into play that can become hits) but recent advances in defensive positioning has led to fewer balls in play safely landing for hits. This particularly impact team opponent batting average (as opposed to batting average against for individual pitchers) as teams generally enact defensive shifts regardless which of their pitchers are on the mound.