Lots of inexperience.
Mariota was one of five Titans rookies on the field - including right tackle Jeremiah Poutasi, right guard Andy Gallik subbing while Jamon Meredith dealt with cramping, wide receiver Dorial Green-Beckham and fullback Jalston Fowler.
The youngsters played with determination.
Fowler scored the touchdown that gave Tennessee a chance at a tying 2-point conversion only to be tackled for a big loss.
So even though blowing a 13-point lead and losing 35-33 to the Colts certainly hurts, coach Ken Whisenhunt is looking at the positives for a team he says could easily be 3-0 instead of 1-2.
''As you go through these situations, you learn from them,'' Whisenhunt said Monday. ''Make no mistake about it: We've got to win one of these games when we get into these situations, and I believe we're going to do it.''
The Titans have enough to fix during their bye before they host Buffalo on Oct. 11.
Mariota was intercepted twice by the Colts, though Whisenhunt said they will ask the NFL to look at the first in a turnover the coach believes was a catch by Delanie Walker and then a fumble. They fell behind a second straight game, this time trailing 14-0. They racked up six more penalties, and wide receivers have to locate the sideline better to finish catches.
They also settled for two field goals when they could have had touchdowns. Antonio Andrews' 13-yard TD run was wiped out by a holding call in the second quarter, and they couldn't convert on first-and-goal at the Colts 1 late in the third.
Defensively, they have allowed too many deep passes. A week after giving up two big touchdown passes to Johnny Manziel in Cleveland, the Titans allowed Andrew Luck to find a receiver for a 48-yard reception and a 35-yard TD - both on third-and-20.
''It's tough, but we'll learn from it,'' Mariota said after the game. ''Proud of the guys in the locker room for fighting all the way through, but it's one of those things. We had a chance to finish it but you know, you've just got to learn from it and get better.''
Center Brian Schwenke said the Titans are tired of learning.
''It's about winning every play, no matter what play is called,'' Schwenke said. ''We should win the game, and we didn't do that.''
With the loss, the Titans missed a chance at sole possession atop the AFC South. But they are showing signs of being much improved over a year ago when they went 2-14 and managed only 254 points all season long.
At this point last year, the Titans scored only 43 points through three games. Now they have 89 points and rank fourth behind only Arizona (17), New England (14) and Buffalo (13) for most touchdowns scored this season with 12. They also are averaging 375.7 yards total offense, good for ninth so far.
Every AFC South team is 1-2, and the Titans return from their bye with three straight home games in October. They also host Miami (1-2) and Atlanta (3-0).
''The thing that's important for us is we can see that we're a better football team,'' Whisenhunt said. ''If we get some of these things cleaned up, we can get on a stretch and win some games and see where that takes us.''
Notes: Whisenhunt said Fowler, who limped off after being hit hard on the 2-point conversion run, will be OK. ... Starting CB Jason McCourty (groin) should be available against Buffalo. NT Sammie Hill (right knee) also may return to practice next week.
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