I have only experienced this once and that was only a couple of days ago, I am however using the latest avast beta, 4.7.971 and on XP Pro 32 bit.
Something and I know not what that was cause web shield to effectively hang, terminating the provider didn't achieve, the service was still running in Task Manager. Unlike you I went to the Administrator Tools, Services and stopped it there and then restarted it at the same place. I had to restart the Web Shield provider also and everything back to normal and no recurrence since then.
What version of avast are you using ?
Does this happen on a regular basis ?
Even at present in you image the CPU of 53% seems high, what were you doing at the time ?
Mine CPU drops to 00 when not actively browsing like it is whilst compiling this reply, see image.