One of the effects of the rule change in starting kickoff positions is that it makes onside kicks a considerably better bet. When you add a 15-yard penalty to the equation, teams should consider making an onside kick a fairly standard play.
There have already been four kicks from the 50 yard line this year. None have been onside. Onside kicks need to go at least 10 yards, but historically they have averaged 13 yards. A regular kick from the 50 yard line will almost certainly result in a touchback. According to the WP model, drives that start at the 20 yard line are worth 0.34 expected points.
From the kicking team's perspective, that is -0.34 points. If the kicking team fails to recover the onside kick, they can expect their opponent to start the drive at the 37 yard line. That would be worth -1.25 EP. If an onside kick was successful, the kicking team would start at their opponent's 37 yard line. That would be worth 2.84 points. A successful onside kick is worth 3.18 points more than the value of the touchback (2.84 minus -0.34). An unsuccessful onside kick is worth -0.91 points (-1.25 minus -0.34). Clearly, a team should attempt an onside kick if they think they have anywhere near a 50% chance at success.
If the kick is a surprise, the kicking team will have a 60% chance of success. That makes the decision to kick onside worth 1.54 points ((3.18 * 0.6) + (-0.91 * 0.4)). This is a very significant gain. It’s roughly the same as completing a 27 yard pass in the middle of the field. By the same token, the decision not to kick the onside kick could be viewed as costing the team an equivalent amount.
Of course, this relies on the kick being a surprise. Since hardly anyone kicks onside from any field position unless desperate, the first few kicks would almost certainly be surprises. Ultimately, if teams always kicked onside from the 50, onside kicks from the 50 would cease being surprises.
If the kick is expected, the math is different. The receiving team would start to expect them and would act accordingly. Of course, the receiving team must show their hand before the kicking team shows its hand. The primary difference between an expected and a surprise onside kick is personnel. The "hands team" that expects onside kicks is made up of small wide receivers. The normal team is made up of large blockers. A kicking team can simply view the receiving team's personnel and call an audible: onside kick if the normal unit is in place, regular kick if the hands team is in place. Expected onside kicks are successful only 20% of the time. In this case, an onside kick will be worth -0.09 points ((3.18 * 0.2) + (-0.91 * 0.8)). If the kick is expected, the kicking team should not kick onside.
However, it should be noted that when you start at the 50 yard line, even an expected onside kick has very little cost. It equates to about one yard in the middle of the field. The cost of attempting an onside kick from the 50 even when the opponent has its full hands team out in complete expected mode is very trivial.
I would recommend that any team that is behind kick an onside regardless of whether the hands team is in place. The potential gain of following one score with recovering the ball in opposition territory is large enough to outweigh the slight expected point differential. By the same rough logic, a team should kick away if they are already winning and facing the opposition's hands team.
The circumstances that dictate a normal kick to a normal return team are extremely limited. It might seem odd to attempt an onside if you are leading by one point and there is a minute to go. This is actually the correct strategy from the 50 yard line. It’s a similar situation to Belichick's famous fourth down decision. The opportunity to completely end the game right then and there is worth more than the cost of the lost yards.
If teams started maximizing expected value, the game would evolve. One piece of evolution would be that there would never be any reason for the receiving team not to have their hands team on the field after a 15-yard penalty. A regular kick will almost certainly not be returned, so traditional blockers are useless. You are giving the kicking team too great an opportunity. You should expect an onside kick in those circumstances.
I imagine that it will take some time, but eventually coaches will see this logic. I suspect we'll see this situation arise quite frequently. We've already had four kicks from the 50 in the first two weeks. At that pace, we'll have 34 in the regular season. It will be interesting to see who is the first coach to attempt an onside kick. It will also be interesting to see how many are attempted. I have no doubt that the coach that tries it will be viewed as a gambler. It’s not gambling when the odds are on your side. The fact is that if you stop and think about it, all the other coaches are gamblers. Why give up a legitimate opportunity to get the ball deep in opposition territory in exchange for 17 yards of field position? That’s the real gamble and it’s not a smart one.