Back turned

Back turned (BT) is a generic stance entered when your back is towards the opponent. During BT it isn't possible to guard or do any normal moves. Sidestepping is less evasive and turns around. Jumping has normal behavior but it isn't possible to hop.

Crouch

You can crouch during BT by holding D to crush highs. However, doing so will never enter any crouching stances, so the moves you can do are the same regardless of how long you've been crouching for.

Generic BT moves

BT.1_2_1+2 - 8f high, -8 / +3 / +3 15dmg
BT.3_4 - 10f high, -8 / KND W! / KND W! 18dmg
BT.d+1_2 - 10f special mid -2 / +9 / +9 10dmg
BT.d+3_4 - 10f low, -11 / +3 / +3 12dmg
BT.uf+3 - 17f mid, -12 / KND / KND 25dmg
BT.uf+4 - 17f mid, -12 / Launch / Launch 18dmg

Turning around

All attacks and throws turn around immediately. Throws are safer since they aren't likely to eat a counter hit.
6^[1] frames to turn and block by holding forward - this lasts for 18^[untested] frames until you have to again hold back to continue blocking.
7 frames to turn and block with holding back
9^[untested] frames to turn and block with db,B - this enters crouch state on frame 1 and thus high crushes.

↑ It takes 7 frames to turn and block if the animation of the attack leaves the 3D model in a neutral back turned state (e.g. Yoshimitsu's f,f+1+2). If the animation favors a specific side (e.g. Yoshimitsu's ws2), turning from that side reduces the time to 6 frames.

Lists

Moves that force BT on the opponent:

Lucky Chloe df+1+2 throw
Xiayou CH f,F+3
Generic jump over tech trap

Moves that recover BT:

Law b+4~b, b+3~b, 2,b+2~b
Lili f,f+4~b, b+2,1~b, df+2~b
Armor King 3+4

Characters that can manually enter BT:

Feng (b+3~4)
Hwoarang (1+2, has both generic BT and Right Foot Forward BT ((RFF BT))
Kunimitsu (b+3+4)
Lei (b+3+4)
Lili (b+3+4)
Lucky Chloe (b+3+4)
Master Raven (b+3+4)
Xiaoyu (b+3+4, called Rain Dance Stance (RDS))
Yoshimitsu (3+4, called Meditation (MED))

BT Table

This table highlights characters that lack certain generic BT moves, regardless of the input. All generic BT moves are accessible to the rest of the cast.

Character	BT.1_2_1+2	BT.3_4_3+4	BT.d+1_2_1+2	BT.d+3_4_3+4	BT.uf+3	BT.ub+4	BT.u+4	BT.uf+4
Akuma	No	No	No	No	No	No	No	No
Armor King	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes
Eliza	No	No	No	No	No	No	No	No
Feng	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Geese	No	No	No	No	No	No	No	No
Kunimitsu	No	No	Yes	Yes	Yes	Yes	Yes	Yes
Law	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Lei	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Lucky Chloe	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes
Master Raven	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Noctis	Yes	Yes	Yes	Yes	No	No	No	No
Steve	Yes	No	Yes	No	No	No	No	No
Xiaoyu	No	Yes	Yes	No	Yes	Yes	Yes	Yes

[info-1] It takes 7 frames to turn and block if the animation of the attack leaves the 3D model in a neutral back turned state (e.g. Yoshimitsu's f,f+1+2). If the animation favors a specific side (e.g. Yoshimitsu's ws2), turning from that side reduces the time to 6 frames.

[1]