So a site you monitor experiences a MASSIVE traffic drop on the date of a noteworthy Google update. Your first thought is “they got slammed by this update”, right?
You may be wrong.
The other day I was looking in on a few sites which I no longer actively support but that I check in on from time to time. Imagine my surprise when I saw this on a formerly-healthy site:

The huge drop was on July 17, 2015 – the data Panda 4.2 began rolling out. As of February 2016, Google analytics was no longer receiving data. Looking at the site, I found it was now being redirected to an affiliate offer. This site had been showing growth – what the hell went wrong and why did they abandon ship?
Popping it into Barracuda’s Panguin Tool, the data correlates to a severe Panda 4.2 slap, supported by a small drop correlating with Panda 4.1 back in 2014. (There’s also a temporary blip around the Pigeon update, but this is not a local site.) Things had been looking up since January, 2015 and traffic was showing a nice increase following the second Phantom /Quality Update in May 2015.

It seemed like an awfully harsh Panda slap for this site – being reduced to having no Google traffic at all! I headed back to Analytics to see what was going on in Bing, et al only to find that ALL their organic AND direct traffic – everything except referral spam – had dropped off the map on 07/17/2015.

Long story short, it wasn’t Panda. In this case, the site owner had “done something.” A very bad “something.”
Encouraged by the traffic growth of April through June and a modest number of sales they were getting through an affiliate offer on the site, they redirected the site directly to the affiliate offer, thinking they’d capitalize on the increased traffic.
I can’t even begin to list all the ways in which this thinking was wrong, but the worst of it was that they also 404’d all of their inner pages – and only 25% of their organic traffic had been going to the home page!

NB: The offer performed better when visitors first had a chance to first browse the information on-site.
TL;DR
Here are the takeaways:
- Even if a traffic drop looks like it absolutely, positively MUST be the result of some corresponding algo update, check it out thoroughly, never assume. This example was an outlier, but hopefully it gets the point across. If you try to rectify a problem that doesn’t exist, you’re likely to make things worse.
Search penalty expert Marie Haynes has posted an exhaustive list of other reasons for a traffic drop which covers situations you’re much more likely to run into in real life. - Your home page isn’t necessarily the page driving the most traffic. It may just be a small slice of the pie. Keep that in mind when deleting or redirecting things.
- Killing off your site when it’s just starting to grow and flourish is a REALLY bad idea!