When is it ne-waza?

In all these positions the blue athlete can touch the leg.

Both athletes must have two knees on the floor, for it to be considered ne-waza.

No contact between the opponents must be mate!

Lying on the stomach on the ground, the blue athlete is in ne-waza.

If the blue athlete has two elbows and two knees on the floor the white athlete can do a technique only to transition into ne-waza. From this position a throw cannot be considered for a score.

What is ne-shisei?

White athlete, from these positions can throw his opponent but the attack must be done immediately.

Grip control from standing athlete (white): we still consider athlete on the knees (blue) in tachi-waza and consequently tachi-waza regulation would be applied. 

However, if white does not attack immediately, then the referee must call mate! Athlete on the knees (blue) cannot grab the legs to defend the throw with his arms, if this happens, shido will be given. 

Nage-waza valid situation

In this position tori can apply a throwing technique and can continue with kansetsu-waza  or shime-waza or osaekomi-waza (not shown) after a real attack or a counter attack.