The clash happened overnight in a Serbian enclave in Northern Kosovo. Serbs clashed with KFOR --NATO Kosovo Force--as they tried to remove barricades set up by the Serbs. The standoff has been ongoing since Kosovo tried to send border police to the north last July.
The Serbian government is under pressure from the European Union to remove the barricades or risk the failure of its candidacy for future membership in the Union. Given the state of the European Union that might not be a huge loss for Serbia.
A more pressing issue for the Serbian government is that the opposition supports the Serbs in the enclave very strongly. The government may lose votes if it gives in to EU pressure. Even though the government is pro-Western it may be hesitant to do anything that could rouse Serb nationalists against them.
Serbia lost control of Kosovo in 1999. Formerly Kosovo was part of Serbia and before that Yugoslavia. NATO bombed Serbia for 78 days after an attempt by then leader Milosevic to expel Albanians from Kosovo. After the Albanian separatist insurgency won there was in effect a cleansing of Serbs and other non-Albanians from Kosovo except that in the north a Serbian majority enclave remains.
Kosovo declared independence unilaterally and was recognized by more than 80 countries even though the terms of independence were supposed to be negotiated with Serbia. For more see this article.