Two meanings, either robbery or cadging/wheedling something for free,as below:

blag [blæg] Slang
n
a robbery, esp with violence
vb blags, blagging, blagged (tr)
1. to obtain by wheedling or cadging she blagged free tickets from her mate
2. to snatch (wages, someone's handbag, etc.); steal
3. to rob (esp a bank or post office)

I was using it in the sense of the "1" meaning...not suggesting he held a gun to anyone's head :-)