Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: OIivier Giroud and Theo Walcott's battle for Arsenal's striking berth is emerging as one of the most intriguing rivalries of the season. There have been great player rivalries over the years – Cesc Fabregas and Frank Lampard, Diego Costa and Martin Skrtel, Roy Keane and Patrick Vieira, Alan Shearer and Alf-Inge Haaland – but they are generally found between players from opposing sides (Lee Bowyer and Kieron Dyer aside). But manager Arsene Wenger has made it clear that Giroud and Walcott are being pitted against each other to lead the line and the players are well-aware of their situation. The England forward has started the last five games, scoring twice, but Giroud has come from the bench to replace him each time and scored twice in the previous two matches.Arsene Wenger has been opting between Theo Walcott and Olivier GiroudWalcott has impressed for Arsenal in a more central berth this seasonGiroud has been effective coming on as a substitute in the last two gamesWenger admits the pair are in competition with one another to start up frontGiroud says he has never experienced a situation in his career such as thisArsenal's Plan B: Arsene Wenger has swallowed his pride and let top teams have possession... and it's reaping big rewards 
 Question:But recently Wenger has subverted that theory, letting _ repeatedly run in behind the backline then introducing Giroud to give their wary opponents a physical challenge to deal with.

Theo Walcott