@lars330 Ok so, cos I can't fit this in a regular tweet. Red player is Innovation, arguably the best Terran player overall in the world. The blue player is Ryung, a Terran vs Terran specialist with a good record against Innovation and a master of strategy in that match up. Ryung executed a rush with Reapers, jump-jet units that are fast, can throw grenades and traverse cliffs to bypass defenses. It had done a lot of damage and Innovation was on the ropes. The momentum would have likely continued and resulted in a win for Ryung. However, Innovation is able to get a single defensive unit out, a Cylone, a mechanized rocket launcher basically, which immediately opens fire on the Reapers. Normally, a Cyclone does not beat 4 reapers in a straight up fight, however, since it surprised Ryung he tried to pull back to regroup. Reapers can regenerate their health after a short time so had he done that, he'd have been able to continue the assault and probably win from there. In Starcraft, a unit will take the shortest possible path to a destination, but it will not auto-correct if the route to that destination becomes obstructed, you have to do that yourself by clicking again. Ryung attempts to retreat to regroup.

At that very split second, Innovation selects his barracks, the big red building that constructs infantry units and tells it to start construction of an add-on, in this case a tech-lab, which immediately starts. He does this JUST as the Reapers are trying to retreat, blocking their escape and causing a momentary lapse of control for Ryung which is enough for the Cyclone to destroy the Reapers and turn a game he was losing badly into a game he went on to win.

It's impressive because the timing required to do that is split second. If he'd done it too early, while the Reapers were further away, Ryung would have immediately either changed their direction or focused fire on the Cyclone, killing it and continuing his rampage. If he'd done it too late, as in, a few milliseconds later than he did, the Reapers would have escaped without casualties. If the Reapers had escaped, he'd have come back shortly after with full health and more reaper reinforcements, you can see in the top left he was building 2 more Reapers at that time. Innovation would have almost certainly lost the game had that happened.

Innovation turned the tide with just a single unit and an incredible split-second feat of dexterity and decision making. This is why some people regard him as the best Starcraft 2 player right now and arguably ever.