When it comes to determining how accurate a quarterback is, the first stat we typically look at is completion percentage. It gives us an idea, but it shouldn't be taken as a complete picture. The QB could have a completion percentage of 70 percent, but what if he's throwing mostly short passes?

Conversely, what if it's only 57 percent, but he's typically attempting longer passes? Or what if their receivers keep dropping balls?

All of this is why I'm a fan of Sports Info Solutions' On-Target Percentage for QBs. It doesn't record whether the pass was caught as much as whether or not it was, you guessed it, on target. For this week's Friday Five, I went through the numbers of returning QBs in 2019 to try and find guys who may have been victimized by circumstance last season and could be more accurate than their numbers indicate.

In other words, these could be guys on the precipice of taking a step forward in 2019 if the luck evens out. Of course, no matter what they say, luck doesn't always even out.

We'll start with a terrifying reality.

5. Tua Tagovailoa, Alabama: Last season, Tagovailoa led the nation in passing efficiency while throwing for 3,966 yards, 43 touchdowns and only 6 interceptions before finishing as the runner-up in both the Heisman Trophy ceremony and national title game. And he could have been better. Tua completed 69.01 percent of his passes last season for 11.2 yards per attempt, but his on-target rate was even better at 78.87 percent, which is 9.86 percent higher than his completion rate. He did all this while averaging 5.40 air yards per attempt (an air yard is every yard past the line of scrimmage a throw goes, so if the LOS is the 35, and the pass is caught at the 41, it's 6 air yards). Of 134 FBS QBs with at least 150 pass attempts last season, that ranks fifth.

So what happened? Well, it wasn't his receivers. Alabama receivers had a drop rate of only 5.5 percent last season, which ranked 12th in the nation. Odds are that Tagovailoa ran into some good defense and they broke up passes that were on target, or just kept the receivers from being able to make the catch. Whatever the case, if Tagovailoa maintains the accuracy he showed last season, and more of his passes are completed, all while still taking big shots down the field, he could put up some ridiculous numbers. Or, I guess I should say more ridiculous numbers.

4. Tyler Huntley, Utah: Huntley makes this list for a few reasons, with the biggest being the overall accuracy of his throws. Of all the returning starters I went through to put this together, none had a higher on-target rate than Huntley's 82.55 percent. But his completion percentage last year was only 64.26 percent. That's a difference of 18.29 percent. A lot of that is because Utah's receivers had a drop rate of 9.6 percent last season, which is entirely too many drops.

Still, I don't know how much of a leap Huntley can be expected to make in 2019. While he was unlucky with his throws, he averaged only 3.51 air yards per throw, which ranked 86th among the 134 QBs with at least 150 pass attempts. It's far less challenging to be accurate on shorter throws than longer ones, which helps explain Huntley's on-target rate. Still, a difference of 18.29 percent is enormous, and if luck evens out, Huntley's overall numbers should look better in 2019. That would be good news for a Utah team hoping to contend for a Pac-12 title.

3. Jarrett Guarantano, Tennessee: Are you a Tennessee fan who has been trying to convince others that Jarrett Guarantano is better than his overall numbers looked last season? If you are, I have good news. You might be right!

Guarantano completed 62.20 percent of his passes last season for 1,907 yards, 12 touchdowns, and 3 interceptions. He also averaged 7.8 yards per attempt, which ranked 36th nationally. All good signs that become better signs when we find other numbers that tell us they could have been stronger numbers.

Guarantano's on-target rate was 79.67 percent last season, with an average of 4.11 air yards per attempt (51st of 134). Tennessee receivers had a drop rate of 8.4 percent, which isn't horrific, but certainly isn't good. Guarantano could be in line for a nice step forward in 2019.

2. KJ Costello, Stanford: I worry about what Stanford's offense will look like without J.J. Arcega-Whiteside catching everything within 10 feet of his body, but after looking at Costello's numbers last season, there's reason for optimism. Costello played well last year, passing for 3,540 yards and 29 touchdowns to go with 11 interceptions. His average of 8.6 yards per attempt ranked 11th nationally. But while his completion rate was at 65.13 percent, his on-target rate was 11.14 percent better at 76.27 percent. Costello also averaged 5.57 air yards per attempt, which ranked 4th amongst the 134 QBs with 150 attempts, ahead of even Tagovailoa.

There's concern that Stanford's drop rate of 4.1 percent will increase without Arcega-Whiteside, but considering the Cardinal's offensive philosophy of intellectual brutality, and their use of play-action, Costello should continue being very effective in 2019. Possibly even better than we've already seen.

1. Brock Purdy, Iowa State: Is Matt Campbell's offense magic, or is Purdy really good? Maybe it's a combination of both? Last season, Purdy threw for 2,250 yards and 16 touchdowns in 10 games, while averaging 10.2 yards per attempt as a freshman. His passing efficiency rating of 169.91 finished third in the Big 12 behind only Kyler Murray and Will Grier, which is pretty good company to keep. Of course, Purdy, freshman that he was, also threw 7 interceptions, so it wasn't all perfect.

But he could have been better with a little more luck.

Not only did Purdy rank second of the 134 QBs with at least 150 pass attempts in air yards per attempt with 5.92 (only Kyler Murray's 6.02 was better), but his on-target rate of 82.11 ranked second amongst the returning QBs I considered for this list, trailing only Huntley. His completion percentage was 66.51 percent, 15.60 percent lower than his on-target rate. While Hakeem Butler was an excellent safety valve that allowed Purdy to chuck the ball up sometimes, Cyclones receivers finished the year with a drop rate of 8.7 percent. That's not good, and Butler was the biggest culprit (he had a drop rate of 15.2 percent). If Iowa State receivers do a better job of pulling Purdy's passes in, he might have himself a monster season that could vault him into the Heisman conversation.

Honorable Mention: Jake Bentley, South Carolina; Charlie Brewer, Baylor; Joe Burrow, LSU; Trevor Lawrence, Clemson