Hit confirming is the ability to react to cues to know if a move hit, counter hit, or got blocked. In case of CH it's called counter hit confirming.
This is important, as moves cause different situations on hit and block. Generally if a move gets blocked - you lost your turn, and shouldn't press more buttons, unless you really want to. Launchers often have more difficult versions for a combo due to the difficulty of hit confirming it, as an example after a successful magic 4 there might be a very tight follow-up, which isn't that hard in practice, but in the actual situation one has to react very quickly to perform the combo, thus an easier follow-up is often preferred.
But mainly hit confirming refers to strings guaranteed to hit if one of the first hits connected. Often without confirming the strings are very punishable. There are several ways of confirming:
Hit spark & Hitstun
When a move gets blocked, you see white sparks, when a move hit, and the move dealt less than 20 damage, you see red sparks, on counter hit moves deal additional damage, possibly exceeding 20 damage, causing the big spark, that you can customize in-game.
Some characters have strings with natural hit properties and delayable parts, which is rare in Tekken. Characters like the Mishimas can press 1,1 and see by the hitstun(not exclusive to the hit spark) if the character blocked or no, and visually confirming into 2, which is guaranteed on hit. The visual cues generally are very consistent, but requires very delayable hits for proper confirming, especially when it goes for counter hit confirming vs hit confirming, to avoid any mistake. Examples:
- Mishima 1,1<2 (You can delay the second 1 into 2)
- Bryan d/f+1,1,1<1,2 (the 2 cannot be delayed but the 1 can, so you use/delay the first three hits to confirm into 1,2)
- Lei Wolf Rush f,n,4,1,2,3 (2 can be confirmed naturally but 3 only on Counter Hit)
- Law f,F+2<3 (A single hit with delay to confirm into 3)[* 1]
Some moves have a explosive or very distinguishable sound effect, sometimes helped by a zoom of the camera(e.g. Steve b+1), confirming normal hit is very easy because blocking sound is so different. On counter hit some moves cause a loud unmistakable sound effect, also helping counter hit confirming strings. Examples:
- Lei b+4,1
- Zafina d+4,3
- Steve b+1
when the confirmable move is barely delayable if at all, the only cue you might get enough in advance or at all is if opponent's body moved at all near the time of hit, chances are - they were trying to do a move, and thus it was a counter hit. By far the most inconsistent, it's recommended only strings which aren't too much negative or punishable on block. Examples:
- Lei Razor Rush f,n,1,2,1,2
- Sidestep into immediate d/f+1 string
similar to spark cue, some moves cause different opponent animation depending on if they got hit, or got counter hit. Can be more inconsistent depending on the animation, and also requires very delayable hits. Examples:
- Zafina d+1,1
Some moves have a bigger recovery on whiff instead if it was blocked, being locked on a longer animation and sometimes on a recognizable pose or animation. You generally will be searching for whiffs with movement, baiting for attacks while you focus on your opponent and how he will react to your actions.