While the potential absence of four key contributors will undoubtedly impact the offense in the short-term, it is the season-ending loss of Clark that will alter the way the unit operates going forward.
Clark, who led all tight ends with 37 receptions prior to his injury, is the X-factor in the offense. Though he is listed as a tight end, the team uses him in an H-back role to create mismatches in space. When used as part of the "12" personnel package (one running back, two tight ends and two receivers), Clark floats between being aligned as a conventional tight end or displaced as a slot receiver. While he possesses the size of a prototypical tight end (6-foot-3, 252 pounds), his receiving skills make defensive coordinators have to decide whether to shadow him with a linebacker, safety or nickel back.
The Colts complicate matters by using a no-huddle attack that limits defensive substitutions and forces the opponent to stay in a selected package for the entire series, which creates a huge advantage for the offense. If the defense stays in its base package, Manning will spread the field and attack the favorable matchup. This often places Clark at the top of the pecking order, but it also creates opportunities for Pierre Garcon and Reggie Wayne based on where the defense directs the double team.
If the defense shuttles its nickel package on the field, the Colts jump into their double-tight end formation to run or use a series of play-action passes to push the ball down the field.
Given the versatility and explosiveness of Indy's "12" package with Clark, the Colts potentially lose out on several big-play opportunities with his replacements, Jacob Tamme and Brody Eldridge, on the field. Neither is regarded as a major receiving threat, and defenses will no longer make stopping the tight end a focal point.
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Without Clark to create mismatches out of double-tight end sets, the Colts go back to more three- and four-receiver formations in passing situations. This would normally put Collie in a position to pick up some of the slack, but his thumb injury will keep him out for the next few weeks, so Anthony Gonzalez and Blair White will be part of the Colts' four-receiver sets. While neither is regarded as a difference-maker, they are capable of making enough plays collectively to keep the offense rolling.
Of course, the loss of Clark will encourage more teams to use two-deep coverage to limit the amount of downfield throws from Manning. However, his willingness to take the checkdown not only counters that tactic, but increases the role of the running back as a receiver. With Addai and Brown ailing, Mike Hart could see a number of balls head on dumpoffs. If Hart is able to muster a few first downs, defenses will eventually clamp down on the shorter routes, which, in turn, will open up the field for the vertical game.
The Colts have been considered a title contender due to Manning's presence, but their fortunes this season hinge on replacing their most dynamic offensive weapon. With a tough road to navigate through the AFC, Indianapolis must hope that one of its unheralded players is ready to take on a lead role for the team to retain its spot at the postseason table.