I will be surprised if no action is taken against both of the fan that threw the coin/s, and Walcott.
Walcott was immature in his celebration to the Spurs crowd. Adebayor was penalised for his action in celebrating ahead of the Arsenal fans, why was Walcott's actions any different? He incensed our fans and that carries a punishment as far as I'm aware.
The fans who threw the coins over reacted, there is no way that the behaviour of Walcott should have led to physical violence. I can understand the frustration and annoyance that Walcott caused but sometimes in life, we have to be more tolerant.
If the fans hadn't reacted, it would have been far more likely that Walcott would have received a penalty. As it is, sympathy may carry for Walcott and no further action be taken.
Walcott acted like a dingdong, he obviously knew he would get stick off our fans and so reacted as he thought he could. There aren't many who could resist temptation to react in a similar way to Walcott, especially not as a youngster; Walcott is only 24, he still needs to mature a bit.
So both parties are guilty and penalties should be considered, and applied if applicable,