[Number4]

It's case of differing interest. The Red Sox want a quality established player, they want him now and they want him for cheap (in terms of salary). That doesn't come cheap in terms of prospects.

The White Sox want to get rid of Sale, mostly for rebuilding reasons, maybe added with a small bit of "he cut our jerseys!". But a quality starting pitcher will always get a lot of trade value, therefore a good offer has to be made. But still, the longer you hold on to Sale, the less value will he have as he'll be closer to free agency, so they'd prefer to trade now.

In an ideal world, the trade would profit both sides. The Red Sox will use the quality only a great pitcher as Sale can provide to go very far, maybe all the way, in the playoffs, raking in money from additional games and additional fans.

The White Sox would waste Sale's best years with a mediocre team, so they hope the prospects will get them better value when they are ready to compete with a better team.

As the trade of "value now" versus "value later" is in mutual interest, I assume the trade is roughly balanced, in that the front offices more or less think the Red Sox gave up as much future expected value in the prospects as they got in Sale now.

But prospects are a crapshoot, and you might get them being brilliant, or fizzle out. You have to judge the trade now, not whether the Red Sox have traded the future MVP for a Tommy John surgery pitcher, or traded a bunch of career minor leaguers for a Cy Young winner.

And I think now, it is fair.