In this first picture the slide is going to the defensive left. The RG is the first uncovered linemen and starts the slide. The RG will block any rusher in the A gap. Similarly the C, LG, and LT are in the slide and will block the rusher in the A, B, and C gaps respectively. The RT is man blocking the DE.
In the second picture the slide is still going to the left but this time the defense is in a G front with the RG covered. Therefore the C is the first uncovered lineman and starts the slide with the LG and LT also sliding. The RG is man on the Nose and the RT is once again man on the DE.
The RB is stepping to the man side and is responsible for 1 to 2 (Dual Read on the ILB and OLB in this 4-4 look). He will block inside out after which he may check release into a route or look to help in the protection elsewhere.
The QB is responsible to throw hot if both the ILB and OLB to the slide blitz. If only 1 blitzes the offense feels the slide protection should be able to pick it up. Similarly if both the ILB and OLB to the man side blitz the QB should throw hot. Many offensive coordinators tell the QB vs 8 potential rushers (4-4 & 3-5) to key the safety if you see blitzers creeping and a safety coming down that is the side were you need to throw hot.
In the following series of posts I will diagram some blitz stratagies to attack 1/2 slide protection.