First, I've noted this a few times around here, but it's a common misconception that the Western Front was one continuous battle. Daytime shelling and nighttime sniping were common, but as a general rule, the front experienced low-intensity fighting punctuated by high-intensity battle (a la the Somme, Verdun, etc.). Moreover, shell shortages were being felt pretty severely by the winter of 1914, and both sides were hunkering down, improving their defenses, and building ammunition stores in preparation for new offensives in the spring. Winter in Flanders is not a good time to launch attacks because the ground is wet and muddy.

Second, the trench lines around where this supposed football match happened were still quite new and not yet fully developed by the standards of 1916-17. The British and German armies only began digging in around Ypres in mid- to late October, and only since mid-November did the fighting calm down enough for them to really get to work on defenses. There was lots of barbed wire out, but it was still in pretty short supply in 1914, and not until spring was it plentiful in the British army.

To sum up, then, in 1914, no man's land wasn't a cratered moonscape covered in layers and layers of barbed wire and pillboxes. Moreover, the Western Front was not, contrary to popular imagination, a place of constant, relentless grinding and combat.

Sources: Beckett, Ypres 1914; Dykstra, "Entrenchment, Field Fortifications, and the Learning Process in the BEF"