An Objective-C method to compute NFL passer rating.

NFLQuarterback.h

#import <Foundation/Foundation.h>

#define NUMBER_IN_RANGE(num, floor, ceiling) ((num >= floor && num <= ceiling) ? num : ((num < floor) ? floor : ceiling))

@interface NFLQuarterback
@property (nonatomic, strong) NSNumber *completions;
@property (nonatomic, strong) NSNumber *interceptions;
@property (nonatomic, strong) NSNumber *touchdowns;
@property (nonatomic, strong) NSNumber *yards;
@property (readonly) NSNumber *passerRating;
@end

NFLQuarterback.m

#import "NFLQuarterback.h"

@implementation NFLQuarterback
@dynamic completions;
@dynamic interceptions;
@dynamic touchdowns;
@dynamic yards;

// Defines a function which handles passer rating calculation for the NFL.
- (NSNumber *)passerRating {
	float rating;
	
	// Step 1: Completion percentage
	float completionPercentage = ([self.completions floatValue] - 0.3) * 5.0;
	completionPercentage = NUMBER_IN_RANGE(completionPercentage, 0, 2.375);
	rating += completionPercentage;
	
	// Step 2: Yards per attempt
	float yardsPerAttempts = ([self.yards floatValue] - 3.0) * 0.25;
	yardsPerAttempt = NUMBER_IN_RANGE(yardsPerAttempt, 0, 2.375);
	rating += yardsPerAttempt;
	
	// Step 3: Touchdown percentage
	float touchdownPercentage = NUMBER_IN_RANGE([self.touchdowns floatValue] * 20, 0, 2.375);
	rating += touchdownPercentage;
	
	// Step 4: Interception percentage
	float interceptionPercentage = 2.375 - (self.interceptions * 25);
	interceptionPercentage = NUMBER_IN_RANGE(interceptionPercentage, 0, 2.375);
	rating += interceptionPercentage;

	// Step 5: Voodoo
	rating = (rating / 6) * 100;
	
	// Step 6: Return an NSNumber of the passer rating
	return [NSNumber numberWithFloat:rating];
}
@end

I should note that I have not actually tested this code. Should be close enough though.