Should away teams be more aggressive?

The Portland Timbers traveled to Houston on Sunday in desperate need of three points to get out of the cellar in the Western Conference. They played well in the first half, outshooting the Dynamo 8 – 7 en route to a 1 – 1 tie, while dominating possession. Then Portland came out in the second half much like many away teams do with a tie score, conservatively. The second-half shot charts to the right serve as an indication of the change in strategy.  

This conjured up a question that constantly bugs me. Should away teams go for wins more often when tied in the second half? Let's get right to the data. Here is chart summarizing the offensive aggression of away teams during gamestates when the score is tied and the teams are playing with the same number of players. The data presents the proportion of totals earned by the away team in both the first and second halves.

2013-14	Goals	xGoals	Shots
1st Half	44.8% (266)	42.3% (282.9)	43.4% (2948)
2nd Half	34.8% (184)	37.4% (168.6)	39.7% (1654)
P-value	0.017	---	0.007

The away team consistently garners 42% to 45% of these primary offensive stats during the first half, and then drops down to the 35%-to-40% range in the second half. For the proportions of goals and shots, those differences are statistically significant (there is no simple test for xGoals%, but it is probably statistically significant as well).

My instinct is that away teams are capable of playing in the second half as they do in the first half, and that these discrepancies are a product of conscious decision making by away coaches and players. Teams likely change strategy in the second half to preserve a tie. Playing more openly would ostensibly increase the chances of both a loss and win, while decreasing the chances of a tie. However, I would think based on the data above that it would increase the chances of a win more so than the chances of a loss. Since a win would earn the away team an extra two points, while a loss would cost it just one, my gut says teams should go for it more often.

Are away teams playing conservatively because mindless soccer conventionality tells them that it's okay to get one point on the road? Is this the self-detrimental risk aversion that plagues coaches in other sports, or are these numbers missing something that could justify the conservative play?

I can't say that I've proven anything, but these data suggest the former.