That's a new paper by Edward Miguel, Sebastian Saiegh, and Shanker Satyanath and here is the abstract:
In recent years scholars have begun to focus on the consequences of individuals’ exposure to civil war, including its severe health and psychological consequences. Our innovation is to move beyond the survey methodology that is widespread in this literature to analyze the actual behavior of individuals with varying degrees of exposure to civil war in a common institutional setting. We exploit the presence of thousands of international soccer (football) players with different exposures to civil conflict in the European professional leagues, and find a strong relationship between the extent of civil conflict in a player’s home country and his propensity to behave violently on the soccer field, as measured by yellow and red cards. This link is robust to region fixed effects, country characteristics (e.g., rule of law, per capita income), player characteristics (e.g., age, field position, quality), outliers, and team fixed effects. Reinforcing our claim that we isolate the effect of civil war exposure rather than simple rule-breaking or something else entirely, there is no meaningful correlation between our measure of exposure to civil war and soccer performance measures not closely related to violent conduct. The result is also robust to controlling for civil wars before a player’s birth, suggesting that it is not driven by factors from the distant historical past.
One question is whether such behavior occurs because the player's psyche has somehow been brutalized or whether it is a deliberate affect aimed at a violence-expecting audience back home. It's related to which variables might best predict the propensity of an NBA player to pick up technical fouls; would that be correlated with urban upbringing, the nature of the audience (home vs. away, TV vs. live crowd, etc.) or perhaps correlated with early brushes with the law?
If you wish to skim the results, start with p.25. The Colombian players pick up a lot of yellow cards.